
==== Front
Musculoskelet Surg
Musculoskelet Surg
Musculoskeletal Surgery
2035-5106
2035-5114
Springer Milan Milan

38809336
824
10.1007/s12306-024-00824-2
Original Article
Anterior cruciate ligament reconstruction: effect of graft type and gender on early to mid-term clinical outcomes
http://orcid.org/0000-0002-8317-9864
Mann O. oliver.mann1@nhs.net

1
Al-Dadah O. 23
1 https://ror.org/01kj2bm70 grid.1006.7 0000 0001 0462 7212 The Medical School, Newcastle University, Framlington Place, Newcastle-Upon-Tyne, NE2 4HH UK
2 https://ror.org/00q75av54 grid.416158.f 0000 0004 0417 0998 Department of Trauma and Orthopaedic Surgery, South Tyneside District Hospital, Harton Lane, South Tyneside, NE34 0PL UK
3 https://ror.org/01kj2bm70 grid.1006.7 0000 0001 0462 7212 Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Framlington Place, Newcastle-Upon-Tyne, NE2 4HH UK
29 5 2024
29 5 2024
2024
108 3 313322
16 10 2023
3 5 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by/4.0/ Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
Introduction

Anterior cruciate ligament (ACL) rupture is a debilitating condition and often requires surgery to restore joint stability. Common autografts used for reconstruction include patella tendon and hamstring tendons. The primary aim of this study was to evaluate the early to mid-term clinical outcomes of ACL reconstruction using validated patient-reported outcome measures (PROMs). The secondary aim was to compare clinical outcomes between patella tendon and hamstring tendon autografts. The tertiary aim was to compare clinical outcomes between males and females.

Methods

Patients with an ACL rupture were evaluated before and after surgery using PROM scores which included Lysholm, Tegner, International Knee Documentation Committee (IKDC), Knee Injury and Osteoarthritis Outcome Score (KOOS), Short Form-12 Item (SF-12) and EQ-5D-5L.

Results

A total of 87 patients were included in the study. All PROM scores significantly improved following surgery (p < 0.001) at a mean follow-up time of 28 months (range 12 to 88 months). The patella tendon subgroup (n = 27) had superior post-operative results as compared to the hamstring tendon subgroup (n = 60) for KOOS sport and recreation (p = 0.005), KOOS quality of life (p = 0.025), KOOS overall (p = 0.026), Tegner (p = 0.046) and IKDC (p = 0.021) scores. There was no significant difference of PROM scores between males (n = 60) and females (n = 27) (p > 0.05).

Conclusions

ACL reconstruction significantly improves clinical outcomes for patients with symptomatic instability consequent to ACL rupture. Overall, patella tendon autograft resulted in better clinical outcomes as compared to hamstring tendon autograft following surgery. Gender did not influence clinical outcome following ACL reconstruction.

Keywords

Anterior cruciate ligament reconstruction
Patient-reported outcome measures
Patella tendon
Hamstring tendon
Autograft
Gender
issue-copyright-statement© Istituto Ortopedico Rizzoli 2024
==== Body
pmcIntroduction

Anterior cruciate ligament (ACL) rupture is a debilitating injury which can result in recurrent episodes of knee joint instability and is becoming increasingly prevalent. Consequently, the volume of surgical reconstruction of the ACL in clinical practice is rising too. In England alone, it is estimated that around 15,000 primary ACL reconstructions are performed every year [1]. Current national guidelines in the United Kingdom (UK) state that the main indication for ACL reconstruction is symptomatic instability, and that all patients should be offered prehabilitation prior to their procedures [2]. In most cases, surgery is considered following an initial period of conservative treatment (i.e. physiotherapy) in an attempt to strengthen the peri-articular muscles and provide further stability for the ACL deficient knee. The decision between early surgical reconstruction or a protracted trial of conservative treatment is based on patient preference following an informed decision made in discussion with the surgeon. If recurrent instability persists despite an initial trial of conservative treatment, surgery is then considered. ACL reconstruction can return 65% of patients to the same level of sporting performance following their procedure [3]. The two commonest autografts used for arthroscopic surgical reconstruction include the hamstring tendons (HT), and the patella tendon, also known as a bone-patella tendon-bone (BTB) autograft [4]. The knee joint must be able to go through a full range of movement as a prerequisite to either procedure [2, 5].

These two surgical techniques have well-established advantages and disadvantages. The BTB autograft is thought to be stronger as the natural bone-tendon attachment is very strong, with the potential for bone integration [6], and results in less knee laxity than a hamstring tendon autograft [7]. However, patients having BTB autografts sometimes complain of more severe anterior knee pain post-operatively than those receiving HT autografts [6]. Therefore, patients who do a lot of kneeling in their occupation or for cultural, religious or recreational reasons will tend to receive HT autografts as anterior knee pain would be more debilitating for them [8]. The BTB autograft is thought to have a higher rate of complications, including patella fractures, patella tendon rupture and quadriceps weakness [9, 10]. The HT autograft, although thought to be weaker, can be used to avoid these complications, whilst maintaining the extensor mechanism of the lower limb [6]. Some of the disadvantages of the HT autograft includes a longer biological integration time due to the lack of bone plugs, weakness of the hamstring musculature which means there is reduced stabilisation of the knee joint, potentially making re-rupture more likely [6].

The primary aim of this study was to evaluate the early to mid-term clinical outcomes of ACL reconstruction using validated patient-reported outcome measures (PROMs). The secondary aim was to compare clinical outcomes between patella tendon and hamstring tendon autografts. The tertiary aim was to compare clinical outcomes between males and females. The first hypothesis of this study is that surgical reconstruction will improve clinical outcomes in patients with ACL rupture. The second hypothesis is that no difference exists in terms of clinical outcomes between the two autografts used for surgery. The third hypothesis is that no difference exists between genders regarding clinical outcomes following ACL reconstruction.

Methods

This is a longitudinal observational study. All the patients included in this study attended a specialist knee clinic and underwent ACL reconstruction surgery between 2015 and 2022 following clinical assessment and radiological investigation. This study was exempt from Institutional Review Board (IRB)/Ethics Committee approval as it was a pragmatic study evaluating the existing clinical practice of the senior author (consultant orthopaedic surgeon). This study was registered with the hospital’s Clinical Effectiveness Department (registration number CA10358). This therapeutic research study constituted part of the first author’s Masters dissertation.

Inclusion criteria consisted of patients with an ACL tear whose symptoms where refractory to an initial period of conservative treatment (i.e. physiotherapy, activity modification, etc.) who subsequently underwent an arthroscopic primary, single-bundle ACL reconstruction using either BTB or HT autografts. Exclusion criteria consisted of posterior cruciate ligament (PCL) tear, multi-ligament reconstruction, revision ACL reconstruction and advanced osteoarthritis.

Surgical technique

All patients underwent arthroscopic ACL reconstruction using the anatomic single-bundle technique and subsequently the same structured post-operative physiotherapy rehabilitation programme. Returning back to contact sports was only permitted 12 months post-operatively.

The HT autograft surgery involves harvesting tendons of the gracilis and semitendinosus muscles. A small incision is made over the hamstring insertion (pes anserinus), and the tendons are stripped from the muscle. The hamstring distal insertions on the pes anserinus were preserved, and the tendons were only detached from their proximal musculotendinous junction using a tendon stripper. Once harvested they are whip stitched and then folded over to create a quadrupled hamstring tendon graft. Tunnels (corresponding in size to the harvested graft) are then drilled into the femur (via the transportal technique) and the tibia (using a tibial jig set to 55 degrees), both of which are centred on the native ACL footprint. The graft is then pulled through the tunnels and secured to the femur via suspensory fixation using EndoButton (Smith & Nephew Inc., Andover, Massachusetts, USA) and to the tibia using either polyetheretherketone (PEEK) interference screws (Smith & Nephew Inc., Andover, Massachusetts, USA) or round cannulated interference (RCI) screws (Smith & Nephew Inc., Andover, Massachusetts, USA). The graft was tensioned with the knee in full extension.

The BTB autograft surgery involves an anterior vertical incision centred over the patella tendon. The middle third (10 mm width) of the entire length of the tendon is harvested (sharp dissection with scalpel) along with its attached proximal and distal bone wedges (10 mm width × 20 mm length) from the patella and the tibial tuberosity, respectively, using a miniature oscillating saw. Tunnels (corresponding in size to the bone wedges) are then drilled into the femur (via the transportal technique) and the tibia (using a tibial jig set to 60 degrees), both of which are centred on the native ACL footprint. The graft is then pulled through the tunnels and secured using Softsilk interference screws (Smith & Nephew Inc., Andover, Massachusetts, USA) both in the femur and the tibia. The graft was tensioned with the knee in full extension.

Clinical outcome scores

A total of 6 validated patient-reported outcome measures (PROMs) were used in this study which included the Knee Injury and Osteoarthritis Outcome Score (KOOS) [11, 12], EuroQol-5 Dimension-5 level (EQ-5D-5L) [13–16], International Knee Documentation Committee (IKDC) score [17, 18], Tegner score [19], Lysholm score [19] and the 12-item Short Form survey (SF-12) [20]. PROM data was collected pre-operatively (at the time of the patients' initial outpatient clinic appointment) and post-operatively (the latest point of contact at the time of conducting this study via postal questionnaire). Some of the PROMs have been validated and used in children, including the paeds-IKDC [21, 22] and paediatric KOOS [23, 24]. The Tegner score can also be used in children as it a measure of activity level. Of the 87 patients included in the study, there were two patients under 16 who completed the paediatric PROMs pre-operatively, and then the adult PROMs post-operatively (when aged over 16). There was one patient with missing pre-operative data, who completed the paediatric PROMs post-operatively. There were two patients who completed the pre-op paediatric PROMs but were lost to follow-up post-intervention, and so have no post-op data. These paediatric scores were included in overall data analysis.

Statistical analysis

Plotted histograms with fitted curve lines, box-plots, normal Q-Q plots, and the Shapiro–Wilk statistic were used to test normality of data distribution. All the PROM data (continuous variables) displayed a skewed distribution and therefore the relevant nonparametric statistical tests were used for the data analysis. The level of statistical significance was set at p < 0.05. Statistical analysis was performed using SPSS for Windows version 28.0 (IBM Corp., Armonk, New York).

Results

Table 1 shows the demographics of all the patients included in the study, showing a mean age of 31.5 years, with over twice as many males as females (60:27), and a mean BMI of 27.5. The disproportionately higher number of males reflects the participation in higher risk activities which commonly generate ACL injuries. Figure 1 shows the mechanism of injury of all participants in the study, with the highest number of patients injuring their ACL playing football (n = 41), followed by twisting (n = 8), falling (n = 7), and skiing/snowboarding (n = 6). The mean time between injury and surgery was 24 months.Table 1 Patient demographics of entire study cohort

	(n = 87)	
Age (years) (mean (range))	31.5 (12–62)	
Sex (male: female)	60:27	
Laterality (left: right)	44:43	
Height (cm) (mean (SD))	174.3 (8.8)	
Weight (kg) (mean (SD))	84.1 (18.0)	
BMI (kg/m2) (mean (SD))	27.5 (5.4)	
Associated meniscus tear (yes: no)	70:17	
Meniscus tear location (medial: lateral)	51:38	
SD, standard deviation; BMI, body mass index

Fig. 1 Mechanism of injury of all patients (n = 87)

Clinical outcome scores

Post-operative PROM score completion timeframe was a mean of 28 months (range 12–88). Of the 87 cases that were contactable post-operatively, there were 2 ACL grafts that had re-ruptured (2.4%), one of which was a hamstring tendon graft, and the other a BTB graft. Table 2 shows that all the PROM scores (except the SF-12 MCS subscore) showed a significant longitudinal improvement (p < 0.001) from pre-operative to post-operative results. The Tegner scores represented in this table are Tegner post-injury to Tegner post-operatively. Table 3 shows that the Tegner score changed significantly between all three points of measurement. Pre-injury to post-injury showed a significant decrease (p < 0.001) in activity level associated with ACL rupture, pre-injury to post-op still showed a significant decrease (p < 0.001) implying surgery did not restore patients to their pre-injury sporting activity levels. Post-injury to post-op (p < 0.001) showed a significant increase, indicating that ACL reconstruction is beneficial to restore knee function which allowed for an improvement in activity level.Table 2 Comparison of pre-operative PROMs versus post-operative PROMs of entire study cohort (n = 87)

	Pre-op median (IQR)	Post-op median (IQR)	p valuea	Z	
KOOS pain	61 (50–74)	89 (78–97)	 < 0.001*	−5.7	
KOOS symptoms	57 (43–68)	79 (68–86)	 < 0.001*	−4.7	
KOOS ADL	71 (56–82)	97 (90–100)	 < 0.001*	−5.5	
KOOS sport/rec	30 (15–50)	75 (60–85)	 < 0.001*	−5.2	
KOOS QoL	19 (6–38)	63 (44–75)	 < 0.001*	−6.1	
KOOS overall	48 (36–61)	81 (70–87)	 < 0.001*	−5.8	
IKDC	42 (30–53)	75 (64–86)	 < 0.001*	−6.2	
Lysholm	53 (40–67)	87 (76–91)	 < 0.001*	−6.0	
Tegner	2 (1–3)	5 (4–7)	 < 0.001*	−5.3	
EQ-5D index	0.621 (0.445–0.723)	0.837 (0.728–1)	 < 0.001*	−5.1	
EQ-5D VAS	70 (50–85)	85 (70–90)	 < 0.001*	−3.7	
SF-12 MCS	51 (41–57)	53 (45–58)	0.367	−0.9	
SF-12 PCS	35 (30–41)	54 (47–57)	 < 0.001*	−5.5	
IQR, inter-quartile range, PROM, patient-reported outcome measures; BTB, bone-patella tendon-bone; HT, hamstring tendon; KOOS, knee injury and osteoarthritis outcome score; ADL, activities of daily living; Sport/Rec, sport and recreation function; QoL, quality of life; IKDC, international knee documentation committee score; SF-12, short form 12; MCS, mental component summary; PCS, physical component summary; EQ-5D, EuroQol-5D; VAS, visual analogue score

aWilcoxon signed rank test

*Statistically significant < 0.05

Table 3 Comparison of Tegner activity scores of entire study cohort (n = 87)

Pre-injury median (IQR)	Post-injury median (IQR)	Post-op median (IQR)	p valuea	Z	
8 (7–9)	2 (1–3)		 < 0.001*	−7.1	
8 (7–9)		5 (4–7)	 < 0.001*	−5.8	
	2 (1–3)	5 (4–7)	 < 0.001*	−5.3	
IQR, inter-quartile range

aWilcoxon signed rank test

*Statistically significant < 0.05

Graft comparison

Table 4 shows the demographics of patients in the BTB group and the HT group. The BTB group were slightly older than the HT group. All the BTB group were male patients, whereas the HT group had a more balanced distribution of males and females. The senior author favoured a hamstring autograft for female patients as it resulted in a smaller skin scar and therefore more aesthetically acceptable whilst also restoring knee joint stability.Table 4 Patient demographics of BTB group versus HT group

	BTB group (n = 27)	HT group (n = 60)	
Age (years) (mean (range))	34.6 (18–62)	28.8 (12–56)	
Sex (male: female)	27:0	33:27	
Laterality (left: right)	12:15	32:28	
Height (cm) (mean(SD))	179.9 (7.3)	171.9 (8.1)	
Weight (kg) (mean(SD))	93.4 (16.3)	80.4 (17.6)	
BMI (kg/m2) (mean(SD))	28.7 (4.3)	27.1 (5.9)	
Associated meniscus tear (yes: no)	22:5	48:12	
Meniscus tear location (medial: lateral)	15:13	36:25	
SD, standard deviation; BMI, body mass index; BTB, bone-patella tendon-bone; HT, hamstring tendon

Table 5 shows that overall, there was no significant difference between the BTB group and the HT group pre-operatively (except for the EQ-5D index score only, p = 0.044). Table 5 also shows that the BTB group scored higher than the HT group for KOOS sport and recreation (p = 0.005), KOOS quality of life (p = 0.025), KOOS overall (p = 0.026), Tegner score (p = 0.046) and the IKDC score (p = 0.021). Overall, the BTB group demonstrated superior results as compared to the HT group.Table 5 Between group comparison of pre-operative and post-operative PROMs: BTB group versus HT group

	Pre-operative	Post-operative	
BTB group (n = 27) median (IQR)	HT group (n = 60) median (IQR)	p valuea	Z	U	BTB group (n = 27) median (IQR)	HT group (n = 60) median (IQR)	p valuea	Z	U	
KOOS pain	61(53–75)	58(46–74)	0.345	−0.9	455	92(77–100)	86(77–94)	0.331	−1.0	279	
KOOS symptoms	64(51–74)	54(41–68)	0.112	−1.6	453	82(71–86)	79(67–87)	0.666	−0.4	318	
KOOS ADL	72(61–81)	71(48–85)	0.585	−0.5	542	98(90–100)	94(86–100)	0.284	−1.1	274	
KOOS sport/rec	35(19–50)	30(18–50	0.804	−0.2	477	85(75–95)	75(48–80)	0.005*	−2.8	167	
KOOS QoL	19(6–38)	19(6–38)	0.577	−0.6	486	72(56–88)	56(35–69)	0.025*	−2.2	209	
KOOS overall	50(43–60)	48(35–61)	0.530	−0.6	448	84(76–94)	80(64–83)	0.026*	−2.2	195	
IKDC	38(29–47)	43(30–56)	0.488	−0.7	475	82(71–89)	72(57–77)	0.021*	−2.3	204	
Lysholm	57(42–67)	49(40–67)	0.601	−0.5	476	89(81–93)	86(72–90)	0.144	−1.5	230	
Tegner	2(2–3)	2(1–3)	0.405	−0.8	339	6(5–7)	5(3–6)	0.046*	−2.0	191	
EQ-5D index	0.708 (0.428–0.781)	0.604 (0.471–0.670)	0.044*	−2.0	371	0.837 (0.724–1)	0.795 (0.700–1)	0.566	−0.6	277	
EQ-5D VAS	70(50–88)	65(50–75)	0.447	−0.8	459	90(75–90)	80(65–90)	0.232	−1.2	251	
SF-12 MCS	51(40–58)	48(40–55)	0.390	−0.9	418	53(44–58)	53(46–59)	0.897	−0.1	283	
SF-12 PCS	38(31–46)	34(29–39)	0.145	−1.5	375	55(50–57)	52(42–56)	0.136	−1.5	215	
IQR, inter-quartile range; PROM, patient-reported outcome measures; BTB, bone-patella tendon-bone; HT, hamstring tendon; KOOS, knee injury and osteoarthritis outcome score; ADL, activities of daily living; Sport/Rec, sport and recreation function; QoL, quality of life; IKDC, International knee documentation committee score; SF-12, short form 12; MCS, mental component summary; PCS, physical component summary; EQ-5D, EuroQol-5D; VAS, visual analogue score

aMann-Whitney U test

*Statistically significant < 0.05

Gender comparison

Table 6 shows that overall, there were no significant differences between males and females pre-operatively. Although there was a statistically significant difference for the Tegner score between the two genders (p = 0.012), this did not amount to a clinically significant difference as they both scored median 2.Table 6 Between group comparison of pre-operative and post-operative PROMs: males versus females

	Pre-operative	Post-operative	
Male group (n = 60) median (IQR)	Female group (n = 27) median (IQR)	p valuea	Z	U	Male group (n = 60) median (IQR)	Female group (n = 27) median (IQR)	p valuea	Z	U	
KOOS pain	61 (53–75)	57 (41–64)	0.156	−1.4	480	89 (77–98)	91 (83–97)	0.592	−0.5	370	
KOOS symptoms	61 (50–71)	43 (36–68)	0.096	−1.7	509	79 (68–86)	82 (68–89)	0.443	−0.8	376	
KOOS ADL	72 (57–84)	65 (38–76)	0.084	−1.7	502	97 (88–100)	96 (90–99)	0.468	−0.7	358	
KOOS sport/rec	35 (20–50)	28 (0–40)	0.150	−1.4	414	75 (65–85)	75 (56–81)	0.292	−1.1	329	
KOOS QoL	21 (13–31)	13 (5–38)	0.427	−0.8	535	63 (41–78)	66 (43–69)	0.742	−0.3	384	
KOOS overall	50 (41–61)	42 (27–54)	0.077	−1.8	387	81 (70–88)	82 (73–84)	0.786	−0.3	379	
IKDC	45 (32–54)	36 (22–45)	0.055	−1.9	435	76 (66–87)	72 (64–85)	0.442	−0.8	355	
Lysholm	57 (43–68)	46 (31–64)	0.091	−1.7	438	86 (74–93)	88 (78–90)	0.962	−0.0	384	
Tegner	2 (2–3)	2 (1–2)	0.012*	−2.5	276	5 (4–7)	4 (3–6)	0.034*	−2.1	220	
EQ-5D index	0.620 (0.454–0.735)	0.623 (0.332–0.661)	0.400	−0.8	521	0.837 (0.733–1)	0.837 (0.679–1)	0.464	−0.7	353	
EQ-5D VAS	70 (57–85)	58 (40–76)	0.083	−1.7	444	85 (70–90)	88 (70–91)	0.499	−0.7	353	
SF-12 MCS	52 (41–57)	47 (33–57)	0.372	−0.9	449	53 (47–58)	54 (43–59)	0.966	−0.0	358	
SF-12 PCS	36 (31–44)	33 (26–39)	0.227	−1.2	424	55 (50–57)	52 (45–57)	0.193	−1.3	283	
IQR, inter-quartile range; PROMs, patient-reported outcome measures; BTB, bone-patella tendon-bone; HT, hamstring tendon; KOOS, knee injury and osteoarthritis outcome score; ADL, activities of daily living; Sport/Rec, sport and recreation function; QoL, quality of life; IKDC, international knee documentation committee score; SF-12, short form 12; MCS, mental component summary; PCS, physical component summary; EQ-5D, EuroQol-5D; VAS, visual analogue score

aMann-Whitney U test

*Statistically significant < 0.05

Table 6 also shows that only the Tegner score showed a significant difference between the two genders following ACL reconstruction (p = 0.034), with males (median 5) scoring higher than females (median 4). None of the other PROM scores showed significant differences between the two genders.

Discussion

This study demonstrated that ACL reconstruction significantly improves clinical outcomes in patients with symptomatic ACL rupture. Overall, BTB autograft showed significantly better clinical outcomes as compared to HT autografts post-operatively. Gender did not influence clinical outcome following ACL reconstruction.

There was a significant longitudinal improvement from pre-op PROMs to post-op PROMs, indicating that surgical reconstruction is a beneficial procedure for patients with a ruptured ACL. The only exception was the SF-12 MCS which did not show any significant difference as it is mainly a reflection of the patient’s mental health rather than physical function of the knee. PROMs are a reliable method of quantitatively evaluating the subjective function of patients’ knee symptomatology. This has been shown to be the case in previous studies using KOOS, Lysholm and IKDC scores [25, 26]. Other studies have used PROMs to assess factors contributing to favourable outcomes following ACL reconstruction. Randsborg et al. [25] assessed factors associated with poor outcome following ACL reconstruction, but only used IKDC as their sole outcome measure. Cristiani et al. [26] used KOOS and Lysholm scores as their outcome measures in a similar study. The strength of the present study was the use of a wide range of different validated PROMs (both disease specific and generic health scoring systems) to analyse the data collected. Furthermore, the present study also had a longer follow-up interval than many other studies, which is potentially more relevant when counselling patients on the pros and cons of different graft types, and their outcomes.

The post-operative PROM score analysis in the present study showed that patients in the BTB group had greater self-reported knee function when compared to the hamstring tendon group. In contrast, Cristiani et al. [26] found that the KOOS score was significantly better in four out of the five subscores in favour of hamstring tendon recipients as compared to patella tendon grafts, although they too found no significant difference in Lysholm score between the two graft types [26]. Similarly, Hamrin et al. [27] found that improved post-operative KOOS sport and recreation and Tegner scores were associated with hamstring tendon autografts. Randsborg et al. [25] utilised only the IKDC score and found no difference between graft types; however, in the present study the IKDC was significantly higher in the BTB group. The literature is varied as other studies did not find significant differences between graft types which utilised Lysholm, Tegner, IKDC or KOOS [8, 28]. A meta-analysis comprising data pooled from five studies also concluded that there was no significant difference in functional outcomes or knee stability between BTB and HT grafts [29].

Conversely, a review of 16 different meta-analyses found that patients that received a patella tendon graft had superior static knee stability post-operatively, but a higher rate of complications including anterior knee pain and kneeling pain [30]. BTB grafts have shown more favourable return to sport rates [31, 32], lower incidence of graft failure [33] and superior rotational stability [32] in a number of other meta-analyses, but many did find that BTB grafts were associated with a greater risk of complications [30, 32–34]. However, other meta-analyses have found no significant difference in re-rupture rates [8, 31, 32], and one states there is insufficient evidence to draw conclusions relating to functional outcomes [8].

A meta-analysis comparing 15 studies that evaluated the mid-term outcomes of ACL reconstruction, with a minimum 5-year follow-up, found no significant differences in Lysholm, Tegner, IKDC scores, or return to pre-injury activity levels [33]. The present study, as well as previous studies, show variation in outcomes when comparing BTB and hamstring graft types, implying that there may be other factors influencing these outcomes than solely graft choice.

The tensile strength of different grafts has been evaluated [35], showing that the native ACL of a male has a tensile strength of 70.83N, a patella tendon autograft 405.18N and a hamstring tendon autograft 807.07N. From these values, it would be expected that the hamstring tendon autograft would give the most favourable outcomes. A similar study by Noyes et al. [36] showed that the tensile strength of the native ACL is 1725N, and the central portion of the patella tendon has a tensile strength (2900N) that is significantly greater than both the semitendinosus (1216N) and gracilis (838N) tendons. These findings are contrary to those reported by Mert et al. [35] but support the findings of the present study—a BTB graft is associated with improved clinical outcomes when compared to a hamstring tendon graft. This could be due to an increase in tensile strength of the graft providing a greater level of stability to the knee, as well as the bone plug biological integration of the BTB graft within the graft tunnels of the femur and tibia.

Other grafts that have been used include quadriceps tendon (QT) autografts, semitendinosus tendon (without gracilis tendon) autografts, allografts and synthetic grafts; however, the latter is currently not recommended for routine primary ACL reconstruction [2]. QT grafts have been shown to be comparable in functional and clinical outcomes, with similar rates of graft failure in a meta-analysis of 20 observational studies [37]. A meta-analysis of 15 studies comparing the combination of semitendinosus and gracilis tendon hamstring grafts to semitendinosus alone found the PROM scores and knee laxity measurements showed no significant differences between the two techniques [38].

Allografts are sometimes used in revision ACL reconstruction surgeries, more often than in primary reconstruction, particularly if autograft tissue is found to be inadequate [39]. Nissen et al. [40] conducted a study comparing autograft to allograft use for revision ACLR. They found that allograft use was associated with a 2.2 times higher rate of re-revision than autograft use. At 1-year post-op, allograft patients also had greater knee laxity than those who had received an autograft. However, knee function and clinical outcomes were not significantly different between the two groups [40]. Another study also concluded that allografts had a much higher rate of re-rupture, lower sports function, and inferior PROMs than autograft use [41].

When evaluating gender, it is widely accepted that women are more susceptible to ACL ruptures than men [42]. This is speculated to be due to a number of factors, including a greater Q angle, smaller intercondylar notch, neuromuscular performance characteristics, as well as the influence of the menstrual cycle [43]. It has been concluded that static Q angle is not a good predictor of susceptibility to ACL injury [44]. A more accurate predictor of ACL rupture risk is the frontal plane projection angle, formed by two lines connecting the anterior superior iliac spine (ASIS) to the centre of the patella, and another from the centre of the patella to the midpoint between the two malleoli of the ankle joint [44]. Women are known to have a narrower intercondylar notch than men [45], and this in turn has been shown to significantly increase the risk of ACL rupture [46].

Humans have a protective reflex arc in order to the prevent the ACL rupturing, which involves recruitment of the hamstring muscles to prevent anterior translation of the tibia, in response to the ACL being under stress [43]. In a study by Wojtys et al. [47], it was found that females take significantly longer to generate maximum hamstring torque than males, as well as being weaker when this does occur, making women more likely to suffer an ACL rupture. They also found that muscle recruitment in women was also different to that of men, whereby women relied on quadriceps muscle activation for initial knee stabilisation, instead of the hamstring muscles [47].

Hormone fluctuations and the menstrual cycle have been found to put women at risk of ACL rupture. Slauterbeck et al. [48] found that increased serum oestrogen levels resulted in reduced tensile strength of the ACL, making it more likely to tear. Another study also found that during the ovulatory stage of the menstrual cycle, a greater than expected number of ACL injuries occurred, with fewer than expected occurring during the follicular phase of the cycle [49].

Despite the significant variation in susceptibility of ACL rupture, overall a higher number of men present with ACL injuries than women (as seen in the present study) which is further supported in the National Ligament Registry 2022 report, showing that 69% of ACL reconstructions were performed on male patients [50]. This is thought to be due to the fact that men are more likely to take part in high-risk sports or activities such as football or rugby.

Although all the patients in the BTB group were male, the present study found no significant differences between males and females in terms of PROM scores pre-operatively or post-operatively with the only exception being the Tegner score where males had a slightly higher actively level following surgery as compared to females. There are also a number of previous studies evaluating the impact of gender on PROMs. These have shown no significant differences between males and females receiving patella tendon autografts as evaluated by the Tegner score and Lysholm score [42, 51, 52]. Salmon et al. [53] found the same in patients receiving hamstring tendon autografts that there were no significant differences on self-reported knee function. Therefore, it can be concluded that the significant differences observed in the post-operative data analysis between graft types was not influenced by gender. Previous studies have shown that males have better post-operative PROMs than females in IKDC, EQ-5D and KOOS scores [25, 27, 54, 55] which is contrary to the findings of the present study.

The main limitation of this study was the subjectivity of the PROM questionnaires being completed by the patients themselves. Many of the post-operative PROM data was gathered via posting the questionnaires to the patients. The timeframe of returning the completed forms was protracted in some and none at all in others, the latter thereby reduced the total number of patients eligible to be included in this study. Future studies may have a more timely and higher response rate through the use of electronic versions of the PROM questionnaires. A general limitation of all patient-reported outcome measures is the subjective interpretation of the individual items (questions) by the patients of each instrument (questionnaire). All the PROM forms included a brief paragraph instructing patients on how to correctly complete the questionnaires. Despite this, some patients still fill in the forms incorrectly or leave certain parts blank. In some cases, this may mean that overall end scores cannot be produced and hence leads to missing data. This limitation could also be addressed by using an online version of the forms which would only allow a patient to submit the PROM when all items have been correctly and fully completed.

Conclusion

A significant improvement of clinical outcomes was demonstrated following reconstructive surgery in patients with symptomatic ACL rupture at early to mid-term follow-up. Overall, the outcome of patients who received patella tendon autograft was superior to that of hamstring tendon autograft. Gender did not influence clinical outcome following ACL reconstruction.

Funding

This study did not receive any funding from any source.

Declarations

Conflict of interest

All authors declare that they have no conflict of interest.

Ethical approval

This was a longitudinal observational study which did not require IRB ethics committee approval.

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
==== Refs
References

1. Davies L Cook J Leal J Areia CM Comparison of the clinical and cost effectiveness of two management strategies (rehabilitation versus surgical reconstruction) for non-acute anterior cruciate ligament (ACL) injury: study protocol for the ACL SNNAP randomised controlled trial Trials 2020 21 1 405 10.1186/s13063-020-04298-y 32410697
Davies L, Cook J, Leal J, Areia CM et al (2020) Comparison of the clinical and cost effectiveness of two management strategies (rehabilitation versus surgical reconstruction) for non-acute anterior cruciate ligament (ACL) injury: study protocol for the ACL SNNAP randomised controlled trial. Trials 21(1):40532410697 10.1186/s13063-020-04298-y
2. Bask-Bostaa (2020) Best practice for management of anterior cruciate ligament injuries. https://www.boa.ac.uk/resource/best-practice-book-for-management-of-anterior-cruciate-ligament-injuries.html
3. Gobbi A Francisco R Factors affecting return to sports after anterior cruciate ligament reconstruction with patellar tendon and hamstring graft: a prospective clinical investigation Knee Surg Sports Traumatol Arthrosc 2006 14 10 1021 1028 10.1007/s00167-006-0050-9 16496124
Gobbi A, Francisco R (2006) Factors affecting return to sports after anterior cruciate ligament reconstruction with patellar tendon and hamstring graft: a prospective clinical investigation. Knee Surg Sports Traumatol Arthrosc 14(10):1021–102816496124 10.1007/s00167-006-0050-9
4. Miller MD Operative techniques : sports knee surgery 2008 Philadelphia PA, Saunders/Elsevier
Miller MD (2008) Operative techniques : sports knee surgery. PA, Saunders/Elsevier, Philadelphia
5. Solomon L Warwick DJ NayagamEbscohost S Apley and Solomon's concise system of orthopaedics and trauma 2014 Hoboken CRC Press
Solomon L, Warwick DJ, NayagamEbscohost S (2014) Apley and Solomon’s concise system of orthopaedics and trauma. CRC Press, Hoboken
6. Cerulli G Placella G Sebastiani E Tei MM ACL reconstruction: choosing the graft Joints 2013 1 1 18 24 25606507
Cerulli G, Placella G, Sebastiani E, Tei MM et al (2013) ACL reconstruction: choosing the graft. Joints 1(1):18–2425606507
7. Freedman KB D’Amato MJ Nedeff DD Kaz A Arthroscopic anterior cruciate ligament reconstruction: a metaanalysis comparing patellar tendon and hamstring tendon autografts Am J Sports Med 2003 31 1 2 11 10.1177/03635465030310011501 12531750
Freedman KB, D’Amato MJ, Nedeff DD, Kaz A et al (2003) Arthroscopic anterior cruciate ligament reconstruction: a metaanalysis comparing patellar tendon and hamstring tendon autografts. Am J Sports Med 31(1):2–1112531750 10.1177/03635465030310011501
8. Mohtadi NG Chan DS Dainty KN Whelan DB Patellar tendon versus hamstring tendon autograft for anterior cruciate ligament rupture in adults Cochrane Database Syst Rev 2011 10.1002/14651858.CD005960.pub2
Mohtadi NG, Chan DS, Dainty KN, Whelan DB (2011) Patellar tendon versus hamstring tendon autograft for anterior cruciate ligament rupture in adults. Cochrane Database Syst Rev. 10.1002/14651858.CD005960.pub210.1002/14651858.CD005960.pub2
9. Almekinders LC Moore T Freedman D Taft TN Post-operative problems following anterior cruciate ligament reconstruction Knee Surg Sports Traumatol Arthrosc 1995 3 2 78 82 10.1007/BF01552379 7553013
Almekinders LC, Moore T, Freedman D, Taft TN (1995) Post-operative problems following anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 3(2):78–827553013 10.1007/BF01552379
10. Marder RA Raskind JR Carroll M Prospective evaluation of arthroscopically assisted anterior cruciate ligament reconstruction: patellar tendon versus semitendinosus and gracilis tendons Am J Sports Med 1991 19 5 478 484 10.1177/036354659101900510 1962713
Marder RA, Raskind JR, Carroll M (1991) Prospective evaluation of arthroscopically assisted anterior cruciate ligament reconstruction: patellar tendon versus semitendinosus and gracilis tendons. Am J Sports Med 19(5):478–4841962713 10.1177/036354659101900510
11. Roos EM Lohmander LS The knee injury and osteoarthritis outcome score (KOOS): from joint injury to osteoarthritis Health Qual Life Outcomes 2003 1 64 10.1186/1477-7525-1-64 14613558
Roos EM, Lohmander LS (2003) The knee injury and osteoarthritis outcome score (KOOS): from joint injury to osteoarthritis. Health Qual Life Outcomes 1:6414613558 10.1186/1477-7525-1-64
12. Roos EM Roos HP Lohmander LS Ekdahl C Knee injury and osteoarthritis outcome score (KOOS)–development of a self-administered outcome measure J Orthop Sports Phys Ther 1998 28 2 88 96 10.2519/jospt.1998.28.2.88 9699158
Roos EM, Roos HP, Lohmander LS, Ekdahl C et al (1998) Knee injury and osteoarthritis outcome score (KOOS)–development of a self-administered outcome measure. J Orthop Sports Phys Ther 28(2):88–969699158 10.2519/jospt.1998.28.2.88
13. Brookes R EuroQol: the current state of play Health Policy 1996 37 1 53 72 10.1016/0168-8510(96)00822-6 10158943
Brookes R (1996) EuroQol: the current state of play. Health Policy 37(1):53–7210158943 10.1016/0168-8510(96)00822-6
14. EuroQol G EuroQol–a new facility for the measurement of health-related quality of life Health Policy 1990 16 3 199 208 10.1016/0168-8510(90)90421-9 10109801
EuroQol G (1990) EuroQol–a new facility for the measurement of health-related quality of life. Health Policy 16(3):199–20810109801 10.1016/0168-8510(90)90421-9
15. Bilbao A Garcia-Perez L Arenaza JC Garcia I Psychometric properties of the EQ-5D-5L in patients with hip or knee osteoarthritis: reliability, validity and responsiveness Qual Life Res 2018 27 11 2897 2908 10.1007/s11136-018-1929-x 29978346
Bilbao A, Garcia-Perez L, Arenaza JC, Garcia I et al (2018) Psychometric properties of the EQ-5D-5L in patients with hip or knee osteoarthritis: reliability, validity and responsiveness. Qual Life Res 27(11):2897–290829978346 10.1007/s11136-018-1929-x
16. Greiner W Weijnen T Nieuwenhuizen M Oppe S A single european currency for EQ-5D health states. Results from a six-country study Eur J Health Econ 2003 4 3 222 231 10.1007/s10198-003-0182-5 15609189
Greiner W, Weijnen T, Nieuwenhuizen M, Oppe S et al (2003) A single european currency for EQ-5D health states. Results from a six-country study. Eur J Health Econ 4(3):222–23115609189 10.1007/s10198-003-0182-5
17. Irrgang JJ Anderson AF Development and validation of health-related quality of life measures for the knee Clin Orthop Relat Res 2002 402 95 109 10.1097/00003086-200209000-00009
Irrgang JJ, Anderson AF (2002) Development and validation of health-related quality of life measures for the knee. Clin Orthop Relat Res 402:95–10910.1097/00003086-200209000-00009
18. Irrgang JJ Anderson AF Boland AL Harner CD Development and validation of the international knee documentation committee subjective knee form Am J Sports Med 2001 29 5 600 613 10.1177/03635465010290051301 11573919
Irrgang JJ, Anderson AF, Boland AL, Harner CD et al (2001) Development and validation of the international knee documentation committee subjective knee form. Am J Sports Med 29(5):600–61311573919 10.1177/03635465010290051301
19. Tegner Y Lysholm J Rating systems in the evaluation of knee ligament injuries Clin Orthop Relat Res 1985 198 43 49 10.1097/00003086-198509000-00007
Tegner Y, Lysholm J (1985) Rating systems in the evaluation of knee ligament injuries. Clin Orthop Relat Res 198:43–4910.1097/00003086-198509000-00007
20. Ware J Jr Kosinski M Keller SD A 12-item short-form health survey: construction of scales and preliminary tests of reliability and validity Med Care 1996 34 3 220 233 10.1097/00005650-199603000-00003 8628042
Ware J Jr, Kosinski M, Keller SD (1996) A 12-item short-form health survey: construction of scales and preliminary tests of reliability and validity. Med Care 34(3):220–2338628042 10.1097/00005650-199603000-00003
21. Boykin RE McFeely ED Shearer D Frank JS Correlation between the child health questionnaire and the international knee documentation committee score in pediatric and adolescent patients with an anterior cruciate ligament tear J Pediatr Orthop 2013 33 2 216 220 10.1097/BPO.0b013e3182745439 23389579
Boykin RE, McFeely ED, Shearer D, Frank JS et al (2013) Correlation between the child health questionnaire and the international knee documentation committee score in pediatric and adolescent patients with an anterior cruciate ligament tear. J Pediatr Orthop 33(2):216–22023389579 10.1097/BPO.0b013e3182745439
22. Kocher MS Smith JT Iversen MD Brustowicz K Reliability, validity, and responsiveness of a modified international knee documentation committee subjective knee form (Pedi-IKDC) in children with knee disorders Am J Sports Med 2011 39 5 933 939 10.1177/0363546510383002 21068443
Kocher MS, Smith JT, Iversen MD, Brustowicz K et al (2011) Reliability, validity, and responsiveness of a modified international knee documentation committee subjective knee form (Pedi-IKDC) in children with knee disorders. Am J Sports Med 39(5):933–93921068443 10.1177/0363546510383002
23. Ortqvist M Iversen MD Janarv PM Brostrom EW Psychometric properties of the knee injury and osteoarthritis outcome score for children (KOOS-Child) in children with knee disorders Br J Sports Med 2014 48 19 1437 1446 10.1136/bjsports-2013-093164 24837242
Ortqvist M, Iversen MD, Janarv PM, Brostrom EW et al (2014) Psychometric properties of the knee injury and osteoarthritis outcome score for children (KOOS-Child) in children with knee disorders. Br J Sports Med 48(19):1437–144624837242 10.1136/bjsports-2013-093164
24. Ortqvist M Roos EM Brostrom EW Janarv PM Development of the knee injury and osteoarthritis outcome score for children (KOOS-Child): comprehensibility and content validity Acta Orthop 2012 83 6 666 673 10.3109/17453674.2012.747921 23140110
Ortqvist M, Roos EM, Brostrom EW, Janarv PM et al (2012) Development of the knee injury and osteoarthritis outcome score for children (KOOS-Child): comprehensibility and content validity. Acta Orthop 83(6):666–67323140110 10.3109/17453674.2012.747921
25. Randsborg PH Cepeda N Adamec D Rodeo SA Patient-reported outcome, return to sport, and revision rates 7–9 years after anterior cruciate ligament reconstruction: results from a cohort of 2042 patients Am J Sports Med 2022 50 2 423 432 10.1177/03635465211060333 35040694
Randsborg PH, Cepeda N, Adamec D, Rodeo SA et al (2022) Patient-reported outcome, return to sport, and revision rates 7–9 years after anterior cruciate ligament reconstruction: results from a cohort of 2042 patients. Am J Sports Med 50(2):423–43235040694 10.1177/03635465211060333
26. Cristiani R Sarakatsianos V Engstrom B Samuelsson K Increased knee laxity with hamstring tendon autograft compared to patellar tendon autograft: a cohort study of 5462 patients with primary anterior cruciate ligament reconstruction Knee Surg Sports Traumatol Arthrosc 2019 27 2 381 388 10.1007/s00167-018-5029-9 29955930
Cristiani R, Sarakatsianos V, Engstrom B, Samuelsson K et al (2019) Increased knee laxity with hamstring tendon autograft compared to patellar tendon autograft: a cohort study of 5462 patients with primary anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 27(2):381–38829955930 10.1007/s00167-018-5029-9
27. Hamrin Senorski E Svantesson E Baldari A Ayeni OR Factors that affect patient reported outcome after anterior cruciate ligament reconstruction-a systematic review of the scandinavian knee ligament registers Br J Sports Med 2019 53 7 410 417 10.1136/bjsports-2017-098191 30030283
Hamrin Senorski E, Svantesson E, Baldari A, Ayeni OR et al (2019) Factors that affect patient reported outcome after anterior cruciate ligament reconstruction-a systematic review of the scandinavian knee ligament registers. Br J Sports Med 53(7):410–41730030283 10.1136/bjsports-2017-098191
28. Tauberg B Sever R Kirschner N Hanstein R Anterior cruciate ligament reconstruction in ≤21 year olds: Patellar versus hamstring tendon autografts Orthop J Sports Med 2020 10.1177/2325967120S00216
Tauberg B, Sever R, Kirschner N, Hanstein R et al (2020) Anterior cruciate ligament reconstruction in ≤21 year olds: Patellar versus hamstring tendon autografts. Orthop J Sports Med. 10.1177/2325967120S0021610.1177/2325967120S00216
29. Chen W Li H Chen Y Jiang F Bone-patellar tendon-bone autografts versus hamstring autografts using the same suspensory fixations in ACL reconstruction: a systematic review and meta-analysis Orthop J Sports Med 2019 7 11 2325967119885314 10.1177/2325967119885314 32010729
Chen W, Li H, Chen Y, Jiang F et al (2019) Bone-patellar tendon-bone autografts versus hamstring autografts using the same suspensory fixations in ACL reconstruction: a systematic review and meta-analysis. Orthop J Sports Med 7(11):232596711988531432010729 10.1177/2325967119885314
30. Schuette HB Kraeutler MJ Houck DA McCarty EC Bone-patellar tendon-bone versus hamstring tendon autografts for primary anterior cruciate ligament reconstruction: a systematic review of overlapping meta-analyses Orthop J Sports Med 2017 5 11 2325967117736484 10.1177/2325967117736484 29152522
Schuette HB, Kraeutler MJ, Houck DA, McCarty EC (2017) Bone-patellar tendon-bone versus hamstring tendon autografts for primary anterior cruciate ligament reconstruction: a systematic review of overlapping meta-analyses. Orthop J Sports Med 5(11):232596711773648429152522 10.1177/2325967117736484
31. DeFazio MW Curry EJ Gustin MJ Sing DC Return to sport after ACL reconstruction with a BTB versus hamstring tendon autograft: a systematic review and meta-analysis Orthop J Sports Med 2020 8 12 2325967120964919 10.1177/2325967120964919 33403206
DeFazio MW, Curry EJ, Gustin MJ, Sing DC et al (2020) Return to sport after ACL reconstruction with a BTB versus hamstring tendon autograft: a systematic review and meta-analysis. Orthop J Sports Med 8(12):232596712096491933403206 10.1177/2325967120964919
32. Xie X Liu X Chen Z Yu Y A meta-analysis of bone-patellar tendon-bone autograft versus four-strand hamstring tendon autograft for anterior cruciate ligament reconstruction Knee 2015 22 2 100 110 10.1016/j.knee.2014.11.014 25547048
Xie X, Liu X, Chen Z, Yu Y et al (2015) A meta-analysis of bone-patellar tendon-bone autograft versus four-strand hamstring tendon autograft for anterior cruciate ligament reconstruction. Knee 22(2):100–11025547048 10.1016/j.knee.2014.11.014
33. Zhao L Lu M Deng M Xing J Outcome of bone-patellar tendon-bone vs hamstring tendon autograft for anterior cruciate ligament reconstruction: a meta-analysis of randomized controlled trials with a 5-year minimum follow-up Medicine (Baltimore) 2020 99 48 e23476 10.1097/MD.0000000000023476 33235137
Zhao L, Lu M, Deng M, Xing J et al (2020) Outcome of bone-patellar tendon-bone vs hamstring tendon autograft for anterior cruciate ligament reconstruction: a meta-analysis of randomized controlled trials with a 5-year minimum follow-up. Medicine (Baltimore) 99(48):e2347633235137 10.1097/MD.0000000000023476
34. Chee MYK Chen Y Pearce CJ Murphy DP Outcome of patellar tendon versus 4-strand hamstring tendon autografts for anterior cruciate ligament reconstruction: a systematic review and meta-analysis of prospective randomized trials Arthrosc J Arthrosc Relate Surg 2017 33 2 450 463 10.1016/j.arthro.2016.09.020
Chee MYK, Chen Y, Pearce CJ, Murphy DP et al (2017) Outcome of patellar tendon versus 4-strand hamstring tendon autografts for anterior cruciate ligament reconstruction: a systematic review and meta-analysis of prospective randomized trials. Arthrosc J Arthrosc Relate Surg 33(2):450–46310.1016/j.arthro.2016.09.020
35. Mert A Cinaroglu S Keles H Aydin M Evaluation of autografts used in anterior cruciate ligament reconstruction in terms of tensile strength Cureus 2023 15 6 e39927 37409216
Mert A, Cinaroglu S, Keles H, Aydin M et al (2023) Evaluation of autografts used in anterior cruciate ligament reconstruction in terms of tensile strength. Cureus 15(6):e3992737409216
36. Noyes FR Butler DL Grood ES Zernicke RF Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions J Bone Joint Surg Am 1984 66 3 344 352 10.2106/00004623-198466030-00005 6699049
Noyes FR, Butler DL, Grood ES, Zernicke RF et al (1984) Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions. J Bone Joint Surg Am 66(3):344–3526699049 10.2106/00004623-198466030-00005
37. Tan TK Subramaniam AG Ebert JR Radic R Quadriceps tendon versus hamstring tendon autografts for anterior cruciate ligament reconstruction: a systematic review and meta-analysis Am J Sports Med 2022 50 14 3974 3986 10.1177/03635465211033995 34470509
Tan TK, Subramaniam AG, Ebert JR, Radic R (2022) Quadriceps tendon versus hamstring tendon autografts for anterior cruciate ligament reconstruction: a systematic review and meta-analysis. Am J Sports Med 50(14):3974–398634470509 10.1177/03635465211033995
38. Chin BZ Wee IJY Syn NLX Krishna L Arthroscopic anterior cruciate ligament reconstruction: a meta-analysis comparing semitendinosus alone and semitendinosus with gracilis tendon autografts J Knee Surg 2019 32 8 796 803 10.1055/s-0038-1669950 30206911
Chin BZ, Wee IJY, Syn NLX, Krishna L (2019) Arthroscopic anterior cruciate ligament reconstruction: a meta-analysis comparing semitendinosus alone and semitendinosus with gracilis tendon autografts. J Knee Surg 32(8):796–80330206911 10.1055/s-0038-1669950
39. Vyas D Rabuck SJ Harner CD Allograft anterior cruciate ligament reconstruction: indications, techniques, and outcomes J Orthop Sports Phys Ther 2012 42 3 196 207 10.2519/jospt.2012.4083 22282347
Vyas D, Rabuck SJ, Harner CD (2012) Allograft anterior cruciate ligament reconstruction: indications, techniques, and outcomes. J Orthop Sports Phys Ther 42(3):196–20722282347 10.2519/jospt.2012.4083
40. Nissen KA Eysturoy NH Nielsen TG Lind M Allograft use results in higher re-revision rate for revision anterior cruciate ligament reconstruction Orthop J Sports Med 2018 10.1177/2325967118775381
Nissen KA, Eysturoy NH, Nielsen TG, Lind M (2018) Allograft use results in higher re-revision rate for revision anterior cruciate ligament reconstruction. Orthop J Sports Med. 10.1177/232596711877538110.1177/2325967118775381
41. Wright RW Huston LJ Haas AK Spindler KP Effect of graft choice on the outcome of revision anterior cruciate ligament reconstruction in the multicenter ACL revision study (MARS) cohort Am J Sports Med 2014 42 10 2301 2310 10.1177/0363546514549005 25274353
Wright RW, Huston LJ, Haas AK, Spindler KP et al (2014) Effect of graft choice on the outcome of revision anterior cruciate ligament reconstruction in the multicenter ACL revision study (MARS) cohort. Am J Sports Med 42(10):2301–231025274353 10.1177/0363546514549005
42. Ferrari JD Bach BR Jr Bush-Joseph CA Wang T Anterior cruciate ligament reconstruction in men and women: An outcome analysis comparing gender Arthroscopy 2001 17 6 588 596 10.1053/jars.2001.24686 11447545
Ferrari JD, Bach BR Jr, Bush-Joseph CA, Wang T et al (2001) Anterior cruciate ligament reconstruction in men and women: An outcome analysis comparing gender. Arthroscopy 17(6):588–59611447545 10.1053/jars.2001.24686
43. Lewis T Anterior cruciate ligament injury in female athletes: why are women so vulnerable?: literature review Physiotherapy 2000 86 9 464 472 10.1016/S0031-9406(05)60808-5
Lewis T (2000) Anterior cruciate ligament injury in female athletes: why are women so vulnerable?: literature review. Physiotherapy 86(9):464–47210.1016/S0031-9406(05)60808-5
44. Skouras AZ Kanellopolous AK Stasi S Triantafyllou A Clinical significance of the static and dynamic Q-angle Cureus 2022 14 5 e24911 35698708
Skouras AZ, Kanellopolous AK, Stasi S, Triantafyllou A et al (2022) Clinical significance of the static and dynamic Q-angle. Cureus 14(5):e2491135698708
45. Ireland ML The female ACL: why is it more prone to injury? J Orthop 2016 13 2 1 4 10.1016/S0972-978X(16)00023-4 26955227
(2016) The female ACL: why is it more prone to injury? J Orthop 13(2):1–426955227 10.1016/S0972-978X(16)00023-4
46. Hasoon J Al-Dadah O Knee anatomic geometry accurately predicts risk of anterior cruciate ligament rupture Acta Radiol 2023 64 5 1904 1911 10.1177/02841851231152329 36755362
Hasoon J, Al-Dadah O (2023) Knee anatomic geometry accurately predicts risk of anterior cruciate ligament rupture. Acta Radiol 64(5):1904–191136755362 10.1177/02841851231152329
47. Wojtys EM Huston LJ Taylor PD Bastian SD Neuromuscular adaptations in isokinetic, isotonic, and agility training programs Am J Sports Med 1996 24 2 187 192 10.1177/036354659602400212 8775118
Wojtys EM, Huston LJ, Taylor PD, Bastian SD (1996) Neuromuscular adaptations in isokinetic, isotonic, and agility training programs. Am J Sports Med 24(2):187–1928775118 10.1177/036354659602400212
48. Slauterbeck J Clevenger C Lundberg W Burchfield DM Estrogen level alters the failure load of the rabbit anterior cruciate ligament J Orthop Res 1999 17 3 405 408 10.1002/jor.1100170316 10376730
Slauterbeck J, Clevenger C, Lundberg W, Burchfield DM (1999) Estrogen level alters the failure load of the rabbit anterior cruciate ligament. J Orthop Res 17(3):405–40810376730 10.1002/jor.1100170316
49. Wojtys EM Huston LJ Boynton MD Spindler KP The effect of the menstrual cycle on anterior cruciate ligament injuries in women as determined by hormone levels Am J Sports Med 2002 30 2 182 188 10.1177/03635465020300020601 11912085
Wojtys EM, Huston LJ, Boynton MD, Spindler KP et al (2002) The effect of the menstrual cycle on anterior cruciate ligament injuries in women as determined by hormone levels. Am J Sports Med 30(2):182–18811912085 10.1177/03635465020300020601
50. The National Ligament Registry: The seventh annual report (2022) https://www.uknlr.co.uk/pdf/annual-report-2022.pdf
51. Gobbi A Domzalski M Pascual J Comparison of anterior cruciate ligament reconstruction in male and female athletes using the patellar tendon and hamstring autografts Knee Surg Sports Traumatol Arthrosc 2004 12 6 534 539 10.1007/s00167-003-0486-0 15156305
Gobbi A, Domzalski M, Pascual J (2004) Comparison of anterior cruciate ligament reconstruction in male and female athletes using the patellar tendon and hamstring autografts. Knee Surg Sports Traumatol Arthrosc 12(6):534–53915156305 10.1007/s00167-003-0486-0
52. Ott SM Ireland ML Ballantyne BT Wilson JD Comparison of outcomes between males and females after anterior cruciate ligament reconstruction Knee Surg Sports Traumatol Arthrosc 2003 11 2 75 80 10.1007/s00167-003-0348-9 12664198
Ott SM, Ireland ML, Ballantyne BT, Wilson JD et al (2003) Comparison of outcomes between males and females after anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 11(2):75–8012664198 10.1007/s00167-003-0348-9
53. Salmon LJ Refshauge KM Russell VJ Roe JP Gender differences in outcome after anterior cruciate ligament reconstruction with hamstring tendon autograft Am J Sports Med 2006 34 4 621 629 10.1177/0363546505281806 16382011
Salmon LJ, Refshauge KM, Russell VJ, Roe JP et al (2006) Gender differences in outcome after anterior cruciate ligament reconstruction with hamstring tendon autograft. Am J Sports Med 34(4):621–62916382011 10.1177/0363546505281806
54. Ageberg E Forssblad M Herbertsson P Roos EM Sex differences in patient-reported outcomes after anterior cruciate ligament reconstruction: data from the Swedish knee ligament register Am J Sports Med 2010 38 7 1334 1342 10.1177/0363546510361218 20410376
Ageberg E, Forssblad M, Herbertsson P, Roos EM (2010) Sex differences in patient-reported outcomes after anterior cruciate ligament reconstruction: data from the Swedish knee ligament register. Am J Sports Med 38(7):1334–134220410376 10.1177/0363546510361218
55. Bjornsen E Lisee C Schwartz TA Creighton R Improvement trajectories in patient-reported outcomes between males and females after anterior cruciate ligament reconstruction J Athl Train 2023 58 5 430 436 10.4085/1062-6050-0093.22 35788341
Bjornsen E, Lisee C, Schwartz TA, Creighton R et al (2023) Improvement trajectories in patient-reported outcomes between males and females after anterior cruciate ligament reconstruction. J Athl Train 58(5):430–43635788341 10.4085/1062-6050-0093.22
