Outcome of anterior cruciate ligament reconstruction with emphasis on sex-related differences

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1 Scand J Med Sci Sports 2011 doi: /j x & 2011 John Wiley & Sons A/S Outcome of reconstruction with emphasis on sex-related differences M. Ahlde n 1, N. Sernert 2, J. Karlsson 1, J. Kartus 2 1 Department of Orthopaedics, Sahlgrenska University Hospital, Mo lndal, Sahlgrenska Academy, Gothenburg University, Sweden, 2 Department of Orthopaedics, NU Hospital Organisation, Trollha ttan/uddevalla, Sahlgrenska Academy, Gothenburg University, Sweden Corresponding author: Mattias Ahlde n, MD, Department of Orthopaedics, Sahlgrenska University Hospital, Mo lndal, SE Mo lndal, Sweden. mattias.e.ahlden@vgregion.se Accepted for publication 17 January 2011 The aim of this retrospective study was to compare the results after arthroscopic (ACL) reconstruction using the four-strand semitendinosus-gracilis (ST/G) autograft in male (n 5 141) vs female (n 5 103) patients. The patients were operated on between 1996 and 2005, using interference screw fixation and drilling the femoral tunnel through the anteromedial portal. The preoperative assessments and demographics, apart from age (males 29 years, females 26 years; P ), were comparable at the time of surgery. At 25 (23 36) months postoperatively, no significant differences were found between the study groups in terms of anterior side-to-side knee laxity, manual Lachman test, Tegner activity level, Lysholm knee score, range of motion or donor-site morbidity. Both study groups improved significantly in most clinical assessments and functional scores compared with their preoperative values. Two years after ACL reconstruction using ST/G autografts, there were no significant differences between male and female patients in terms of clinical outcome or functional scores. The risk of rupturing the (ACL) is known to be at least two to five times higher in females, depending on age and the type of sports performed (Gwinn et al., 2000; Prodromos et al., 2007; Renstrom et al., 2008). Risk factors that may predispose for an ACL rupture and differ between the sexes are anatomical factors, such as the width of the notch and the size of the ACL, hormonal factors, as well as neuromuscular properties (So derman et al., 2001; McClay Davis & Ireland, 2003; Chandrashekar et al., 2005; Renstrom et al., 2008). Females have greater general joint laxity, including greater knee laxity compared with men (Huston & Wojtys, 1996; Rozzi et al., 1999), which have been proposed to affect the incidence of ACL rupture (Uhorchak et al., 2003; Myer et al., 2008). In ACL reconstruction, the use of the hamstring (HS) tendon autograft has increased markedly during the last decade and meta-analyses have been conducted to compare HS and bone patella tendon bone (BPTB) autografts in terms of clinical outcome, such as laxity, return to previous level of activity and donor-site morbidity (Freedman et al., 2003; Goldblatt et al., 2005; Biau et al., 2006). Arguments in favor of the HS autograft are less extension deficit and less anterior knee pain and arguments in favor of the BPTB autograft are less knee laxity and possibly fewer graft failures. Furthermore, there is an increased interest in comparing the clinical outcome between males and females after ACL reconstruction in order to find data to recommend sex-based surgical techniques (Barber- Westin et al., 1997; Wiger et al., 1999; Noojin et al., 2000; Ferrari et al., 2001; Ott et al., 2003; Gobbi et al., 2004; Svensson et al., 2005; Salmon et al., 2006; Siebold et al., 2006). Using the BPTB autograft, no major differences in the overall outcome between males and females have been found in either shortor medium- to long-term follow-ups (Barber-Westin et al., 1997; Wiger et al., 1999; Ferrari et al., 2001; Ott et al., 2003). However, patello-femoral problems and pain have been reported to be more frequent in females compared with males after using the BPTB autograft (Aglietti et al., 1993). Several studies have reported increased knee laxity after ACL reconstruction using the HS autograft, especially in females (Corry et al., 1999; Gobbi et al., 2004; Salmon et al., 2006), while sex-based differences in terms of subjective symptoms and return to previous level of activity have been subjects to discussion (Noojin et al., 2000; Salmon et al., 2006). The aim of this retrospective study was to compare the results after ACL reconstruction using ST/G autografts between males and females in terms of clinical outcome and functional scores. The hypothesis was that there would be no significant differences between male and female patients. 1

2 Ahlde n et al. Patients and methods Patients Between November 1996 and November 2005, 567 eligible primary ACL reconstructions were performed at the NU Hospital Organisation, Trollha ttan/uddevalla, Sweden. The exclusion and inclusion criteria are presented in Fig. 1. Surgical technique One senior surgeon (J.T.K.) performed all the reconstructions. Associated intra-articular injuries, such as meniscal injuries and chondral lesions, were addressed at the time of the index operation. Cartilage lesions were debrided and meniscal sutures were performed when applicable. The graft was harvested through a 3-cm incision over the pes anserinus. The tendons were palpated and the sartorius fascia was incised parallel to the fibers of the fascia, just above the more distally inserted semitendinosus (ST) tendon. After the vinculum had been cut under visual control, both the ST and gracilis (G) tendons were harvested with a semi-blunt, semicircular, open tendon stripper (Acufex, Microsurgical Inc., Total amount of ACL/PCL reconstruction, Nov 1996 Nov 2005 (n= 832) Excluded patients (n=265) - Revisions (n=75) - PCL reconstructions (n=39) - MCL/LCL injuries more than +1 (n=18) - Radiographically visible3 osteoarthritis or visible subchondral bone at index operation (n=98) - Other; such as fracture, suture or previous major knee surgery (n= 35) Total amount of eligible primary ACL reconstructions during study period (n=567) Excluded patients (n=323) - Revisions during follow up period (n=31, males=21, females n=10)) - BPTB autograft (n=82) - Contralateral ACL injury before or during study period (n=66) - Early ACL reconstruction (within 2 months (n=4) - Non-available pre or post op data (n= 113) - Incomplete data or wrong follow up period (n=27) Final study cohort (n=244) Males n=141 Females n=103 Fig. 1. Flow chart of inclusion and exclusion criteria. 2

3 Outcome of reconstruction Mansfield, Massachusetts, USA). The tendons were prepared for a quadruple graft. Two no. 5 nonresorbable Ticron (Sherwood Medical, St Louis, Missouri, USA) sutures were used as lead sutures at the distal and proximal ends. Resorbable no. 1 Vicryl (GmbH&Co. KG, Norderstedt, Germany) sutures were used for the modified baseball stitches at the distal and proximal ends of the ST/G graft. The femoral tunnel was drilled through the anteromedial portal and placed at the o clock position in the right knee. The tibial tunnel was placed anterior to the normal posterior cruciate ligament. A 7 mm soft-threaded RCI (Smith and Nephew Inc., Andover, Massachusetts, USA) metal interference screw was used on the femoral side, while a 7 9 mm soft-threaded metal RCI screw was used on the tibial side. All the patients were operated on using the single-bundle technique. After the femoral screw had been inserted, firm traction was applied to the graft during the insertion of the tibial screw with the knee in full extension. Clinical assessments One physiotherapist, who was not involved in the rehabilitation, performed all the pre- and post-operative examinations according to a standard protocol. This physiotherapist was blinded to the aim of the study at the time of the examinations. Preoperatively and at the 2-year follow-up, both groups underwent multiple objective and subjective assessments commonly used in evaluating the outcome after ACL reconstruction, such as the KT-1000 arthrometer examination, the manual Lachman test, range of motion (ROM), one-leg-hop test (Tegner et al., 1986), self-administered Lysholm knee score (Tegner et al., 1985) and Tegner activity level (Tegner et al., 1985). The instrumented KT-1000 arthrometer examination (MEDmetric s Corp, San Diego, California, USA) was performed with the patient in the supine position (Daniel et al., 1985). Both legs were placed on a thigh support with the knees in 301 of flexion. A footrest and a strap around the thighs kept the legs in a neutral position. The arms were placed along the sides of the body and the patient was asked to relax. The instrument was calibrated to zero before each displacement test. The anterior displacement of the tibia in relation to the femur was registered at 89N. The readings of the needle position were only accepted if the needle returned to zero 0.5 mm, when the tension in the handle was released. The uninjured leg was always tested first. At least three measurements of each knee were made and the average value was registered. The ROM was measured to the nearest 51 and a side-to-side difference of 51 was dichotomously classified representing an extension or flexion deficit. The one-leg-hop test was used to evaluate the functional performance and a quotient (%) between the index and uninjured leg was calculated (Tegner et al., 1986). The manual Lachman test was estimated by the examiner as the amount of anterior drawer movement with the knee in of flexion. It was graded as 0, 1(o5 mm), 11 (5 10 mm) or 111 (410 mm), compared with the uninjured contralateral knee. Measurements of loss of or disturbances in sensitivity in the anterior knee region were performed by palpation and were measured in cm 2 (Kartus et al., 1997a, b). The patients were classified dichotomously as having subjective anterior knee pain or not if they registered pain while climbing stairs, sitting with the knee in 901 of flexion and during or after activity. The classification of kneeling discomfort was based on the knee-walking test involving direct loading of the anterior knee region. The patients were not allowed to use any protection or clothing during the test while walking six steps forward on their knees on a hard floor. The test is subjectively classified by the patient as OK, unpleasant, difficult or impossible to perform and has previous been used in several studies (Kartus et al.,1997a, b). Rehabilitation All the patients were rehabilitated according to the same guidelines by their local physiotherapists, permitting immediate full weight-bearing and full ROM including full hyperextension (Shelbourne & Nitz, 1990) However, no external load in open kinetic chain exercises apart from the weight of the operated leg was used during the first six post-operative weeks from 301 to full extension. No rehabilitation brace was used (Kartus et al., 1997a, b). Closed-chain exercises were started immediately post-operatively. Running was permitted at 3 months and contact sports at 6 months at the earliest, provided that the patient had regained full functional stability in terms of strength, co-ordination and balance as compared with the contralateral leg. Statistical analysis Mean and median (range) values are presented when applicable. For comparisons of dichotomous variables between the groups, the chi-square test was used. In terms of both continuous and noncontinuous variables, the Mann Whitney U test was used. The Wilcoxon s signed rank test was used for comparisons of the pre-operative and post-operative data within the study groups. A P-value of 0.05 was considered statistically significant. All P-values are two-tailed. 3

4 Ahlde n et al. Table 1. Demographics Table 2. The cause of injury Ethics The study was approved by the Human Ethics Committee at Gothenburg University. Results Male Female Significance Number of patients Age [years; median(range)] 29 (15 61) 26 (13 53) P Injured side (right/left) 73/68 57/46 P Pre-injury Tegner activity 8 (3 10) 8 (2 10) P scale median (range) Missing values 1 2 Time between the injury and 13 (2 360) 15 (2 276) P index operation [months; median (range)] Missing values 2 Follow-up period [months; 25 (23 34) 25 (23 36) P median (range)] Missing values 1 1 Associated injuries 107 (76%) 85 (83%) P addressed at the time of the index operation or during the follow-up period Meniscal (medial and/or lateral) Meniscal and chondral Chondral 11 8 The study comprised 244 patients of whom 141 were males and 103 females. The groups were comparable in terms of the injured side, cause of injury, time to index operation, time to follow-up and pre-injury Tegner activity level but not in terms of age (male 29 years, female 26 years; P ), (Tables 1 and 2). Three patients developed post-operative septic arthritis; one patient was re-operated on with removal of the graft but had a subjectively acceptable outcome and did not wish to undergo ACL revision reconstruction. The other two patients healed uneventfully after lavage and antibiotics. At the followup, all three patients were kept in the study. Associated intra-articular injuries such as meniscal and chondral injuries, which were addressed at the time of the index operation or during the follow-up period, were registered in 107/141 patients (76%) in the male group and in 85/103 patients (83%) in the female group (ns, Table 1). Fifteen patients underwent meniscal sutures (males, n 5 6; females, n 5 9; ns). The KT-1000 anterior side-to-side difference at 89N and the manual Lachman test revealed no significant differences between the study groups either pre-operatively or at follow-up. Both groups significantly decreased their KT-1000 anterior sideto-side differences (Po0.001 male, Po0.05 female, respectively) and their manual Lachman test (Po0.001 male and female, respectively) between the pre-operative examination and the 2-year follow-up. When the KT-1000 laxity measurements were stratified, 68% of the males and 57% of the females displayed an anterior side-to-side knee laxity of 3 mm or less at follow-up (ns) (Table 4). Both groups improved significantly between the pre-operative and follow-up assessment in terms of the Lysholm knee score, Tegner activity level and the one-leg-hop test (Po0.001, respectively, Table 3). There were no significant differences at follow-up between the study groups in terms of the Lysholm knee score, Tegner activity level and extension or flexion deficits (Table 3). Furthermore, the delta values for the Lysholm knee score, Tegner activity level, one-leg-hop test and the KT-1000 anterior sideto-side difference revealed no significant differences (Table 5). At follow-up, 19% of the males and 22% of the females had returned to their previous Tegner level of activity (ns). The male group had significantly higher values in the one-leg-hop test compared with the female group, both pre-operatively and at followup (P and Po0.001, respectively, Table 3). Fourteen patients had disturbance of the anterior knee sensibility already at the time of the ACL reconstruction (males, n 5 9; missing 5 12; females, n 5 5; missing 5 12). There were no significant differences in terms of knee-walking ability, disturbance in anterior knee sensitivity or subjective anterior knee pain between the groups either pre-operatively or at follow-up. Discussion Male (n 5 141) (missing value 5 1) Female (n 5 103) (missing value 5 1) Significance Contact sport 94 (67%) 62 (60%) P Non-contact 22 (16%) 25 (25%) sport ADL 6 (4%) 5 (5%) Work 7 (5%) 2 (2%) Other 11 (8%) 8 (8%) The overall result of the present study was that there were no significant differences between males and females in terms of clinical outcome, such as knee laxity measurement, Lysholm knee score, Tegner activity level and donor-site morbidity, 2 years after ACL reconstruction using ST/G autografts. The question of whether there are sex-related differences in the overall outcome after ACL reconstruction has been subject to debate, especially after using ST/G autografts (Barber-Westin et al., 1997; Wiger et al., 4

5 Table 3. The functional, objective and subjective results pre-operatively and at the two-year follow-up Male (n 5 141) Female (n 5 103) Pre-operative male vs female Pre-operative Two-year Pre-operative Two-year follow-up follow-up Two-year follow-up male vs female Tegner activity level, median (range) 4 (1 9) 6 (1 10)*** 4 (0 9) 5 (1 9)*** P P Missing values Lysholm knee score, median (range) 73 (24 100) 89 (23 100)*** 66 (22 99) 85 (28 100)*** P P Mean Missing values 1 1 One-leg-hop test (%), median (range) 82 (0 117) 95 (0 162)*** 73 (0 118) 88 (0 113)*** P Po0.001 Mean Missing values Extension deficit 3 (2%) 20 (14%)*** 5 (5%) 21 (20%)*** P P Flexion deficit 71 (50%) 87 (62%)* 58 (56%) 64 (62%) P P Patients subjective evaluation Excellent 48 (34%) 26 (26%) P Good 58 (42%) 47 (46%) Fair 27 (19%) 22 (22%) Poor 7 (5%) 6 (6%) Missing value 1 2 *Po0.05, ***Po0.001, comparison between pre-operative and 2-year follow-up values within the group. Outcome of reconstruction Table 4. Knee laxity assessments according to the KT-1000 arthrometer and manual Lachman tests pre-operatively and at follow-up in males and females Male (n 5 141) Female (n 5 103) Pre-operative male vs female Pre-operative Two-year Pre-operative Two-year follow-up follow-up Two-year follow-up male vs female KT-1000 anterior 89N side-to-side 70 (50%) 94 (68%) 47 (46%) 58 (57%) P P difference 3mm 43 mm 70 (50%) 45 (32%)*** 56 (54%) 44 (43%) Missing values KT-1000 anterior 89N side-to-side 3.3 (3.25) 2.2 (2.0) 3.6 (4.0) 2.9 (3.0) P P difference, mean (median) (range) ( ) ( 5 10)*** ( ) ( 3 10)* Missing values (1%) 36 (25%)*** 1 (1%) 33 (32%)*** P P (26%) 98 (70%) 20 (19%) 65 (63%) (69%) 7 (5%) 75 (73%) 5 (5%) 13 6 (4%) 7 (7%) Missing value 1 *Po 0.05, ***Po0.001, comparison between pre-operative and 2-year follow-up values within the group. 1999; Noojin et al., 2000; Ferrari et al., 2001; Ott et al., 2003; Gobbi et al., 2004; Salmon et al., 2006). To our knowledge, the present study comprising 244 patients is the largest cohort of ACL reconstructions using the ST/G autograft that has been evaluated with the emphasis on sex-related differences. The study groups were comparable in terms of demographics, apart from age at baseline. This difference in age at surgery is in line with reports from national ACL-reconstruction registers (Granan et al., 2009). In the present study, there was a small yet notsignificant difference in the mean anterior side-toside laxity between the study groups in terms of the KT-1000 arthrometer measurement at the 2-year follow-up. Correspondingly, no significant difference was found between the study groups when the KT results were stratified. Previous studies have shown poor correlations between anterior laxity and subjective or functional outcome (Snyder-Mackler et al., 1997; Eastlack et al., 1999; Kocher et al., 2004) and a minor and nonsignificant difference in anterior laxity would therefore be of less interest. Moreover, the manual Lachman test revealed no significant differences between males and females at the 2-year follow-up. Contrary to our findings, Corry et al. (1999) reported increased knee laxity in females in the ST/G group both in the KT-1000 arthrometer 5

6 Ahlde n et al. Table 5. The change (delta) between the pre-operative and the 2-year follow-up assessments Males (n 5 141) Females (n 5 103) Significance males vs females Lysholm knee score Median (range) 15 ( 46 to 68) 19 ( 21 to 72) P Mean Missing values 1 1 Tegner activity level Median(range) 2 ( 6to7) 2( 3to6) P Missing values 1 2 One-leg-hop test (%) Median(range) 12 ( 100 to 13.5 ( 89 to P ) 105) Mean Missing values 2 1 KT-1000 anterior 89N side-to-side difference Median(range) 1.0 ( 15 to 1.0 ( 8to P ) 8.5) Mean Missing values 3 1 measurement at 89N and in the manual Lachman test. However, their finding was secondary to their primary goal of comparing the results after ACL reconstruction using BPTB and ST/G autografts. Furthermore, the difference in laxity between sexes was not seen in the BPTB group. Moreover, in their prospective but non-randomized study of 22 males and 18 females, using Endobutton s and Fastlok s fixation on the femoral and tibial side respectively, Gobbi et al. (2004) reported a small yet significant increase in instrumented knee laxity in females compared with males in the ST/G group. In the study by Gobbi et al. (2004), as in the present study, there were no significant differences in subjective evaluation or functional scores. Furthermore, Gobbi et al. (2004) found a higher deficit in peak torque in females in both flexion and extension strength measurements at both 5 and 12 months postoperatively. In the present study, muscle strength measurements were not performed. In a 7-year follow-up of 143 patients, Salmon et al. (2006) compared males and females after ACL reconstruction using ST/G autografts and interference screw fixation. The exclusion criteria were articular cartilage injury and more than one-third of either meniscus excised. The females had significantly greater knee laxity as measured with the manual Lachman test, pivot-shift test and the KT-1000 arthrometer on all follow-up occasions (1, 2, and 7 years post-operatively), compared with the males. However, no significant sex-related differences were found regarding activity level or subjective function, which is in line with the results of the present study. Furthermore, Salmon et al. (2006) used regression analysis and found that sex was the best predictor of knee-laxity outcome, while the graft size was a poor predictor. In another study, the same authors reported that female patients ran no greater risk of re-injuring their ACL and graft choice did not affect the risk of reinjuring the ACL (Salmon et al., 2005). However, in a recent study, after using the BPTB autograft with a 5-year follow-up of 1,425 patients, Shelbourne et al. (2009) found no significant differences between males and females in terms of re-injuring the reconstructed ACL, even if the females had a higher incidence of ACL injury to the contralateral knee. Noojin et al. (2000) compared the results in 39 males and 26 females, using Endobutton s femoral fixation and tibial post or button fixation of the ST/ G autograft, and found a higher failure rate in females. However, clinical failure was defined as one of the following parameters: a 21manual Lachman test, a 11 or greater pivot-shift test, a greater than 5-mm side-to-side difference on the KT-1000 arthrometer test, or the need for revision ACL reconstruction for repeat injury. Noojin et al. (2000) concluded that using a 11 pivot-shift result as a criterion for failure could be criticized as a limitation, and according to the IKDC classification, a 11 pivot shift is regarded as nearly normal. However, the female patients in their study had a significant decrease in the Tegner activity level from pre-injury to post-operatively, which was not seen in the male patients. The females also reported more pain compared with the males. In the present study, there were no significant differences at follow-up between the study groups in terms of Lysholm knee score or Tegner activity level (Table 3). This is consistent with the findings of Salmon et al. (2006) and Gobbi et al. (2004) but not with the findings of Noojin et al. (2000). In the present study, both study groups improved significantly between the pre-operative and follow-up assessment, but only 19% of the males and 22% of the females returned to their previous Tegner level of activity. This is lower compared with other studies; in their meta-analysis, Yunes et al. (2001) found that about 64% of the patients in the HS group returned to their previous activity level, while in another metaanalysis, Freedman et al. (2003) reported that 65.6% of the patients in the ST/G group returned to their previous activity level. However, the review by Myklebust and Bahr (2005) revealed that return to preinjury activity level is highly variable, between 8% and 82% in reconstructed patients and between 19% and 82% in non-reconstructed patients. In the recently published randomized controlled trial on surgical vs non-surgical treatment of ACL injuries by Frobell et al. (2010), 44% of the early reconstructed patients returned to pre-injury activity level com- 6

7 Outcome of reconstruction pared with 36% in the group where optional delayed ACL reconstruction was performed. In the present study, Lysholm knee score at follow-up (male 5 89, female 5 85) is consistent with the findings of Eriksson et al. (2001a, b) comparing BPTB- and HSautografts, but lower compared with other well designed studies (Laxdal et al., 2005; Kostogiannis et al., 2007). There are several reasons, for instance, retrospective study, non-selected cohort, long time that elapsed between injury and surgery, wide age range and somewhat higher average age than in many previous studies (male 29, female 26). However, in the present study, 76% of the males and 72% of the females subjectively rated their postoperative result as good or excellent, which might imply that factors other than the operated knee may affect the actual level of activity. Apart from problems with the reconstructed knee, common causes of a decrease in activity level are psychosocial and include lack of motivation and fear of re-injury. In a review by Kvist and colleagues, only 36% (range 13 70%) of the patients who reduced their activity level did so because of knee function alone (Kvist, 2004, 2005). In the present study, there were no significant differences between the study groups in extension or flexion deficits, but the frequency of flexion deficits was much higher in both groups compared with extension deficits. As reported in the meta-analysis by Biau et al. (2006) and Goldblatt et al. (2005), loss of flexion is more common after using the ST/G autograft and loss of extension is more common after BPTB grafts. Several previous studies favor the use of the HS autograft instead of the BPTB graft, as it results in less donor-site morbidity (Corry et al., 1999; Eriksson et al., 2001a, b; Ejerhed et al., 2003). Patellofemoral problems and pain have been reported more frequently in females compared with males after using the BPTB graft (Aglietti et al., 1993). Similar results have been reported when using the ST/G autograft (Noojin et al., 2000). The present study revealed no significant differences in donor-site morbidity between males and females in terms of kneewalking ability, disturbance in anterior knee sensitivity or subjective anterior knee pain. This is in line with Salmon et al. (2006) and Gobbi et al. (2004). In several randomized clinical trials comparing the results after using the BPTB and ST/G autografts, sex-related results have been reported, but without any consideration of graft type (Eriksson et al., 2001a, b; Jansson et al., 2003; Sajovic et al., 2006). At a 5-year follow-up of 54 patients, Sajovic et al. (2006) found an increase in anterior side-to-side knee laxity at 134N in females but not in males. On the other hand, in their randomized study, Eriksson et al. (2001a, b) found no sex-related differences in terms of knee laxity at the 2-year follow-up of 154 patients. In the same way, Jansson et al. (2003) found no significant differences in terms of the clinical outcome or arthrometer knee-laxity measurements between males and females at the 2-year follow-up of 99 patients primarily comparing BPTB and ST/G autografts using different fixation methods. With the reservation that these results do not take account of the graft type, they are in line with the results of the present study. Several studies have been conducted after using the BPTB autograft for ACL reconstruction and they have shown no differences between sexes in terms of knee laxity and overall functional outcome (Barber-Westin et al., 1997; Wiger et al., 1999; Ott et al., 2003; Gobbi et al., 2004). However, in their retrospective analysis of 200 patients using the BPTB autograft, Ferrari et al. (2001) reported significantly lower mean manual maximum anterior side-to-side KT-1000 differences in males compared with females, but no differences in the clinical outcome or complication rate. The major strength of the present study is the large sample-size (n 5 244). Further strengths of the present study include the fact that the same surgeon performed all the reconstructions and that the assessments were made by one observer blinded to the aim of the study at the time of the examination, who was also not involved in the surgery or rehabilitation. Both study groups were operated on using the same surgical technique and the same fixation method. Potential weaknesses include the retrospective design and the selection bias, as ACL revision surgery was an exclusion criterion for the study. Furthermore, it might have been better to use the manual maximum test instead of measuring the laxity at 89N when performing the KT-1000 assessments. Perspectives Two years after ACL reconstruction using ST/G autografts, there were no significant differences between male and female patients in terms of clinical outcome or functional scores. This study implies that sex alone should not be decisive when it comes to the use of BPTB or ST/G autografts in primary ACL reconstructions. Key words: ACL, surgery, hamstring tendon autograft, sex, clinical outcome. Acknowledgements Financial support was provided by the Research and Development Department of the Council of Fyrbodal, Region Va stra Go taland, the Western Sweden County Council Research Fund and the Swedish Centre for Research in Sports. 7

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