Suture Anchor Repair of Complete Proximal Hamstring Ruptures: A Cadaveric Biomechanical Evaluation.
Multiple clinical studies have demonstrated that acute and chronic surgical repair results in reliable pain relief, a high degree of patient satisfaction, and the ability to return to athletic activity. (3-6,10-13) The proven benefits of operative intervention have led to a variety of surgical techniques that aim to restore normal muscle-tendon length-tension curve properties and tendon footprint anatomy. Recent studies (1,7,14,15) have described techniques such as transosseous sutures or suture anchors in variable numbers, sizes, and configurations. Some investigators make no mention of the size, number, or configuration of anchors, and there are few biomechanical studies that support one configuration over another. (16) Although numerous studies have shown overall good clinical results, subjective and functional outcomes can potentially be further improved after an in vivo analysis of these various repair techniques. With knowledge of the optimal repair construct capable of withstanding early postoperative loads, improvements in early rehabilitation protocols and longterm clinical outcomes can be achieved.
Therefore, the purpose of the current study was to biomechanically evaluate different suture anchor configurations on the time-zero or initial strength of proximal hamstring repairs. Specifically, we aimed to determine whether suture anchor number or relative anchor size would have a significant effect on cyclic displacement and ultimate load to failure of the proximal hamstring origin after repair. We hypothesized that we would be able to define the optimum suture anchor configuration for the repair and specifically that a larger caliber anchor would achieve a greater biomechanical strength compared to a small suture anchor with the equivalent number of anchors.
Twenty-one fresh-frozen human cadaveric hemi-pelvis to mid-femoral shaft specimens (mean age: 62.5 years; range: 49 to 67 years), with an even gender distribution and no evidence of prior abnormality or injury were used in this study. All specimens were dissected of excess soft tissue, taking care to isolate the hamstring muscles and their proximal tendons. Upon visualization and isolation of the proximal attachments, all other soft tissue was removed from the ischial tuberosity.
The prepared specimens were randomly separated into one of five testing groups. The groups represented five proximal hamstring conditions:
1. intact specimens that served as a control,
2. repair with three small suture anchors (3S),
3. repair with five small suture anchors (5S),
4. repair with three large suture anchors (3L), and
5. repair with five large suture anchors (5L).
Suture anchors designated as small were 2.8 mm diameter (TwinFix[TM] Ti; Smith & Nephew, Inc., Andover, MA), and suture anchors designated as large were 5.5 mm diameter (TwinFix[TM] Ultra Ti, Smith & Nephew, Inc., Andover, MA). All suture anchors were preloaded with non-absorbable number 2 ultra--high-molecular-weight polyethylene sutures (Ultrabraid[TM] suture; Smith & Nephew, Inc., Andover, MA). The variety of testing groups allowed for the study of intact tendon insertion properties and comparisons between anchor size (small anchor versus large anchor) and number of anchors (three anchors versus five anchors). There were five specimens in the control group and in each of the large anchor repair groups, and three specimens in each small anchor repair group.
In the repair groups, specimens underwent a simulated proximal hamstring rupture by sharply releasing the conjoint tendon and semimembranosus tendon from the ischial tuberosity using a #10 scalpel blade. The lateral aspect of the ischial tuberosity was then denuded using a curette and periosteal elevator to ensure a direct tendon to bone repair. In the 3S and 3L repair groups, the suture anchors were evenly spaced along the lateral aspect of the ischial tuberosity in a triangle configuration. The sutures from the proximal two anchors were passed through the conjoint tendon, while the suture from the most distal anchor was passed through the semimembranosus tendon. In the 5S and 5L groups, the suture anchors were inserted along the anatomic tendon footprints in an "X" configuration. The sutures of the proximal two anchors were passed through the biceps femoris, the sutures from the central anchor were passed through the semitendinosus tendon, and the sutures from the distal two anchors were passed through the semimembranosus tendon. There were no instances of cortical fracture or perforation of the far cortex while inserting any of the anchors. An anatomic repair was performed with a modified-Krackow stitch in the tendon using only one limb of each suture to allow for a "pulley technique," reducing the tendon to the anatomic footprint.
The specimens were mounted with the ischium potted in a custom jig and the hamstring tendons oriented longitudinally in a physiologic direction. The musculotendinous junctions of the hamstrings were then secured with a custom-built tendon-grasping clamp attached to the material testing system (MTS) load cell (Fig. 1A). Specimens were tested by use of a cyclic tensile force oriented in a manner representative of in vivo forces. This orientation resulted in distraction and shear forces between the hamstring insertions and ischial tuberosity. Each specimen underwent a single tensile preload of 5 Newtons (N). After a preload was applied, control group specimens were loaded to failure at a rate of 33 mm per second to simulate the rapid eccentric contraction during athletic activity. The failure load and method of tendon failure were recorded for each specimen. Following a 5 N pre-conditioning tensile load, each repair specimen was loaded to 250 N initially. The specimens were then cyclically loaded between 150 N and 350 N at a rate of 1 Hz for 500 cycles, which represented approximately 70% of the failure load of the control tendons. After cyclic loading, images were obtained for the determination of gap formation. If the specimen did not fail during cyclic loading, specimens were loaded to failure at a rate of 33 mm per second.
Throughout testing, gap formation was digitally measured using the change in distance between labels placed on the tendon and the ischium. All measurements were made using Image J software (National Institute of Health, Bethesda, MD). Tendon displacement, maximum load, number of cycles to failure, and mode of failure during cyclic loading were recorded for each specimen. Unpaired t-tests were utilized to compare the results between groups and statistical significance was defined as p < 0.05.
Displacement, number of cycles to initial gap formation and load to failure data for each of the 5 groups is reported in Table 1. The intact specimens (control) achieved a mean load to failure of 501.8 N (SD: 145.3; range: 401 to 723 N), which was not significantly different from those in the 3L (mean: 502.4 N; SD: 100.6 N; p = 0.95) and 5L (mean: 490.8 N; SD: 176.3 N; p = 0.87) groups. The control group had a significantly higher load to failure than the 3S (mean: 284.7 N; SD: 43.4 N; p < 0.05) and 5S (mean: 183.3 N; SD: 56.7 N; p < 0.05) groups. Load to failure in the 3L and 5L groups were both significantly higher compared to the 3S (p < 0.05) and 5S (p < 0.05) groups. Failure was more common at the musculotendinous junction in the control group (Fig. 1B) and at the tendon-bone-suture anchor interface (Fig. 1C).
Group 2 (3S) specimens repaired with three 2.8 mm suture anchors, developed gap formation with initial loading and a mean initial gap formation distance of 3.29 mm (range: 1.36 to 4.84 mm). The overall mean gap formation distance was 10.3 mm (range: 4 to 16 mm) after cyclical loading. The mean load to failure was 284.7 N (range: 245 to 331 N). This load to failure value was found to be significantly lower than the control and both repair configurations using the 5.5 mm anchor (p < 0.05 for all comparisons). The most common mode of failure was at the bone-suture anchor interface.
Repairs in group 3 with five 2.8 mm suture anchors (5S) similarly resulted in gap formation with initial loading. The mean initial gap formation distance was 3.27 mm (range: 1.5 to 5.1 mm), while the mean overall gap formation was 9.9 mm after cyclical loading (range: 6.3 to 17 mm). The mean load to failure was lower than the three 2.8 mm anchor repair at 183.3 N (range: 118 to 220 N), (p = 0.069). Similarly, this load to failure value was also significantly lower than the control and both repair configurations using the 5.5 mm anchors (p < 0.05 for all comparisons). The most common mode of failure was at the bone-suture anchor interface.
Group 4 specimens treated with the three 5.5 mm suture anchor repair (3L) resulted in failures at the tendon-bone-suture anchor interface (Fig. 1C). The mean number of cycles prior to gap formation was 58 cycles (range: 21 to 100 cycles) and mean initial gap formation distance was 0.60 mm (range: 0 to 2.9 mm). The mean gap formation was 5.7 mm after cyclic loading (range: 2.7 to 8 mm). The mean load to failure was 502.4 N (range: 394 to 610 N), which was not significantly different than the intact specimens (p = 0.95). However, it was significantly greater than both repair configurations using the 2.8 mm anchors (p < 0.05 for both comparisons). Interestingly, only two out of five specimens tested failed at the bone-suture anchor interface with only one of the anchors from the repair failing.
Group 5 specimens treated with a five 5.5 mm suture anchor (5L) "X" configuration repair similarly failed at the tendon-bone-suture anchor interface. The mean number of cycles prior to gap formation was 110 cycles (range: 40 to 223 cycles) and mean initial gap formation distance was 0.44 mm (range: 0 to 2.18 mm). The mean gap formation was 5.6 mm after cyclic loading (range: 2.4 to 8.7 mm). The mean load to failure was 490.8 N (range: 255 to 650 N), which was not significantly different than the intact specimens (p = 0.87). However, this load to failure value was significantly greater than both repair configurations using the 2.8 mm anchors (p < 0.05 for both comparisons). Similarly, to Group 4, only one of the specimens tested failed at the bone-suture anchor interface, and again only one of the anchors from the repair showed evidence of being pulled out of the bone.
In summary, a vast majority of the suture anchor repairs failed at the tendon-bone interface. There was a significant difference in cycles to gap formation with all 2.8 mm repairs gapping after placement of the initial 250 N load as opposed to the 5.5 mm repairs demonstrating initial gap formation after 58 and 110 cycles for groups 4 and 5, respectively. The 5.5 mm anchor repairs had significantly greater ultimate loads to failure compared to repairs using 2.8 mm anchors (Group 4: 502.4 N and Group 5: 490.8 N versus Group 2: 284.7 N and Group 3: 183.3 N; p < 0.05) with no significant difference compared to intact controls (Group 1: 501.8 N), (Table 1).
Recent evidence has favored acute repair of complete proximal hamstring tears, particularly in the presence of significant tendon retraction in younger active patients. (8-10,17-19) Several techniques have been described for accomplishing primary repair, including suture anchor fixation on the anatomic ischial footprint using both 5-anchor "X" and 3-anchor configurations. A recent study showed that the anatomic footprint of the semitendinosus and long head of the biceps femoris is oval-shaped and typically measures 2.7 cm proximal to distal and 1.8 cm medial to lateral, while the more lateral semimembranosus tendon footprint is crescent-shaped and measures 3.1 cm proximal to distal by 1.1 cm medial to lateral. (20) The 5- and 3-anchor repair techniques aim to recreate both of these insertions, thereby providing a stable attachment site for primary repair. While short-term clinical outcomes have been reported, few biomechanical studies have been published evaluating the effect of suture anchor size or configuration on the strength of proximal hamstring repair constructs. (21)
Although some studies have shown good restoration of preoperative hamstring strength, this remains an important concern after proximal hamstring repairs. In a series of 11 patients with a mean age of 41.5 years, Klingele and Sallay (4) reported greater than 91% restoration of hamstring strength measured with isokinetic strength testing coupled with a high level of patient satisfaction and return to athletics following surgical repair. Similar outcomes were reported by Wood and colleagues (7) in their review of 72 consecutive cases of proximal hamstring repair. At a mean follow-up of 24 months, treated patients had regained 84% of their hamstring strength and 89% of their hamstring endurance compared to the contralateral side, with 80% returning to their pre-injury level of athletic participation. Most recently, Barnett and coworkers (22) published results on 132 proximal hamstring repairs with a mean follow-up of 53.8 months. At a minimum 2-year follow-up, the repaired hamstring strength was 81.0% and endurance 106.4% compared with the contralateral side. Additionally, 72% of patients returned to pre-injury activity level.
Earlier and more aggressive physical therapy is one potential method to achieve better restoration of strength following surgical repair and earlier return to sports. The strength of the repair construct at time zero theoretically dictates how early and aggressive one can be with postoperative physical therapy. The clinical significance of not obtaining 100% of the hamstring strength after surgical repair is not currently known. However, lack of full strength could potentially have more detrimental effects on the elite athlete whose performance in competition could be limited by this small difference.
A few surgical techniques have been described for primary repair of complete proximal hamstring ruptures. Exposure of the ischial tuberosity and torn hamstring tendons varies slightly in terms of incision, soft tissue dissection, and management of the sciatic nerve. However, once the ischial tuberosity is prepared for suture anchor implantation, techniques generally fall into two categories: five anchor or two to three anchor techniques. Miller and Webb (14) described their two to three anchor technique in which one anchor is placed in the semimembranosus footprint and one or two anchors are used for the semitendinosus and long head of the biceps femoris common tendon origin. In our technique, we use metal corkscrew anchors and a modified-Krackow technique, running the first locking stitch proximal to distal then a second distal to proximal. This is done for each suture anchor, either 3- or 5-anchor configurations. Alternative suture techniques include the Mason-Allen technique and horizontal mattresses. (1,7,14) Some, such as Pombo and Bradley, (15) opt for bio-absorbable suture anchors.
Functional outcome studies have been conducted on both 3- and 5-anchor configurations with generally good results at early follow-up (Table 2). (3-7,10,13,17,18,21,23-25) There are fewer 5-anchor repair outcomes published, yet the construct demonstrates comparable results. (18,24) Smaller suture anchors have been studied more often in the literature, likely due to the limited surface area available for anchor implantation on the ischial tuberosity. To the best of our knowledge, there is only one other published study with data on 5.5 mm anchor performance. (21) Our protocol called for 3- and 5-anchor configurations. Five large anchors were placed without any difficulty. There were no instances of cortical fracture or perforation of the far cortex while inserting any of the anchors.
A recent biomechanical study by Hamming and associates (26) evaluated construct strength of intact controls, two small anchors, two large anchors, and five small anchor repair techniques. Their results showed that the five small anchor configuration demonstrated no significance difference in strength compared with intact controls. Both configurations with two suture anchors, however, proved inferior to the five small anchor and intact specimens. A weakness of their study is that they did not attempt a five large anchor configuration or three suture anchor repair, which is commonly used by some surgeons. Our study demonstrated a difference between sizes and configuration not captured by their study design. Therefore, while our results corroborate the strength of the 5-anchor configuration, our findings also suggest that size of the suture anchor does matter, whether using a 3- or 5-anchor repair configuration. It should also be noted that in their study they were able to obtain loads to failure of 1,405 N for the intact specimen and 1164 N for the five small anchor repair, while in our study our intact specimen had a load to failure of 501.8 N and the repair with the three 5.5 mm suture anchors had a load to failure value of 502.4 N. The differences in these values may be accounted for the differences in the age of our specimens (mean of 54.5 versus a mean 62.5 years old in this current study) and differences in testing protocol. Regardless of these differences, we were able to show that repair with three 5.5 mm suture anchors led to a restoration of a load to failure that was equivalent to our control specimens, which was one of the main objectives of this study.
Our results showed that the larger 5.5 mm suture anchor outperformed the 2.8 mm anchor irrespective of configuration. Both 3- and 5-anchor repairs using the larger diameter suture anchor demonstrated a greater number of cycles before gap formation, decreased gap formation distance, and greater forces required for failure. Given the similar result profile with three and five anchor configurations, we recommend repairing complete proximal hamstring ruptures using the three 5.5 mm suture anchor configuration.
Limitations of the present study include relatively few specimens per subgroup; however, we were able to show statistically significant differences. Furthermore, having an unequal number of specimens in the groups is another potential limitation of the study. However, the fact that the results of our preliminary study showed such a significant difference in the strength of the repairs using the 5.5 mm versus the 2.8 mm anchors, a mid-study analysis found it would be most clinically relevant to only continue testing with the 5.5 mm anchors. No power analysis was conducted prior to study initiation due to limited reference values for hamstring strength at the time our study was initiated. However, we believe we were adequately powered to test the primary hypothesis and draw appropriate conclusions from the results. None of the sizes or configurations tested were significantly stronger than the native tendon. However, it is possible that testing greater numbers of specimens may have changed some of the secondary results we achieved. Another limitation is that our study did not include other types of commonly used sutures anchors, such as non-absorbable polyether ether ketone (PEEK) and absorbable biocomposite anchors; therefore, conclusions regarding the failure of modes of these types of anchors cannot be made. However, our results indicating 5.5 mm suture anchors perform better than their 2.8 mm counterparts could still potentially be applied to these other types of suture anchors. As with all biomechanical studies, the conclusions are only appropriate for time zero of the repair, or initial construct strength, and may not have any bearing on ultimate strength of the construct once tendon to bone healing has occurred.
The current study examines the biomechanical strength of proximal hamstring repairs using suture anchor techniques at time zero. Use of 5.5 mm anchors resulted in a significantly greater ultimate load to failure and significantly less gap formation than that seen following repairs with 2.8 mm anchors. With an initial fixation strength that is similar to intact controls and no difference between 3- and 5-anchor repairs, we believe that our data supports the use of three large suture anchors in the management of complete proximal hamstring ruptures potentially allowing for early active rehabilitation.
Complete proximal hamstring ruptures are best managed with an anatomic three suture anchor repair using 5.5 mm anchors, which are able to restore the biomechanical strength of the proximal hamstring origin.
None of the authors have a financial or proprietary interest in the subject matter or materials discussed, including, but not limited to, employment, consultancies, stock ownership, honoraria, and paid expert testimony.
(1.) Carmichael J, Packham I, Trikha SP, Wood DG. Avulsion of the proximal hamstring origin. Surgical technique. J Bone Joint Surg Am. 2009 Oct 1;91 Suppl 2:249-56.
(2.) Cohen S, Bradley J. Acute proximal hamstring rupture. J Am Acad Orthop Surg. 2007 Jun;15(6):350-5.
(3.) Cross MJ, Vandersluis R, Wood D, Banff M. Surgical repair of chronic complete hamstring tendon rupture in the adult patient. Am J Sports Med. 1998 Nov-Dec;26(6):785-8.
(4.) Klingele KE, Sallay PI. Surgical repair of complete proximal hamstring tendon rupture. Am J Sports Med. 2002 Sep-Oct;30(5):742-7.
(5.) Sallay PI, Ballard G, Hamersly S, Schrader M. Subjective and functional outcomes following surgical repair of complete ruptures of the proximal hamstring complex. Orthopedics. 2008 Nov;31(11):1092.
(6.) Sallay PI, Friedman RL, Coogan PG, Garrett WE. Hamstring muscle injuries among water skiers. Functional outcome and prevention. Am J Sports Med. 1996 Mar-Apr;24(2):130-6.
(7.) Wood DG, Packham I, Trikha SP, Linklater J. Avulsion of the proximal hamstring origin. J Bone Joint Surg Am. 2008 Nov;90(11):2365-74.
(8.) Ahmad CS, Redler LH, Ciccotti MG, et al. Evaluation and management of hamstring injuries. Am J Sports Med. 2013 Dec;41(12):2933-47.
(9.) Harris JD, Griesser MJ, Best TM, Ellis TJ. Treatment of proximal hamstring ruptures--a systematic review. Int J Sports Med. 2011 Jul;32(7):490-5.
(10.) Brucker PU, Imhoff AB. Functional assessment after acute and chronic complete ruptures of the proximal hamstring tendons. Knee Surg Sports Traumatol Arthrosc. 2005 Jul;13(5):411-8.
(11.) Folsom GJ, Larson CM. Surgical treatment of acute versus chronic complete proximal hamstring ruptures: results of a new allograft technique for chronic reconstructions. Am J Sports Med. 2008 Jan;36(1):104-9.
(12.) Puranen J, Orava S. The hamstring syndrome. A new diagnosis of gluteal sciatic pain. Am J Sports Med. 1988 Sep-Oct;16(5):517-21.
(13.) Sarimo J, Lempainen L, Mattila K, Orava S. Complete proximal hamstring avulsions: a series of 41 patients with operative treatment. Am J Sports Med. 2008 Jun;36(6):1110-5.
(14.) Miller SL, Webb GR. The proximal origin of the hamstrings and surrounding anatomy encountered during repair. Surgical technique. J Bone Joint Surg Am. 2008 Mar;90 Suppl 2 Pt 1:108-16.
(15.) Pombo M, Bradley JP. Proximal hamstring avulsion injuries: a technique note on surgical repairs. Sports Health. 2009 May;1(3):261-4.
(16.) Hamming MG, Philippon MJ, Rasmussen MT, et al. Structural properties of the intact proximal hamstring origin and evaluation of varying avulsion repair techniques: an in vitro biomechanical analysis. Am J Sports Med. 2015 Mar;43(3):721-8.
(17.) Birmingham P, Muller M, Wickiewicz T, et al. Functional outcome after repair of proximal hamstring avulsions. J Bone Joint Surg Am. 2011 Oct 5;93(19):1819-26.
(18.) Cohen SB, Rangavajjula A, Vyas D, Bradley JP. Functional results and outcomes after repair of proximal hamstring avulsions. Am J Sports Med. 2012 Sep;40(9):2092-8.
(19.) Ropiak CR, Bosco JA. Hamstring injuries. Bull NYU Hosp Jt Dis. 2012;70(1):41-8.
(20.) Miller SL, Gill J, Webb GR. The proximal origin of the hamstrings and surrounding anatomy encountered during repair. A cadaveric study. J Bone Joint Surg Am. 2007 Jan;89(1):44-8.
(21.) Orava S, Kujala UM. Rupture of the ischial origin of the hamstring muscles. Am J Sports Med. 1995 Nov-Dec;23(6):702-5.
(22.) Barnett AJ, Negus JJ, Barton T, Wood DG. Reattachment of the proximal hamstring origin: outcome in patients with partial and complete tears. Knee Surg Sports Traumatol Arthrosc. 2015 Jul;23(7):2130-5.
(23.) Chakravarthy J, Ramisetty N, Pimpalnerkar A, Mohtadi N. Surgical repair of complete proximal hamstring tendon ruptures in water skiers and bull riders: a report of four cases and review of the literature. Br J Sports Med. 2005 Aug;39(8):569-72.
(24.) Konan S, Haddad F. Successful return to high level sports following early surgical repair of complete tears of the proximal hamstring tendons. Int Orthop. 2010 Feb;34(1):119-23.
(25.) Kwak HY, Bae SW, Choi YS, Jang MS. Early surgical repair of acute complete rupture of the proximal hamstring tendons. Clin Orthop Surg. 2011 Sep;3(3):249-53.
(26.) Hamming MG, Philippon MJ, Rasmussen MT, et al. Structural properties of the intact proximal hamstring origin and evaluation of varying avulsion repair techniques: an in vitro biomechanical analysis. Am J Sports Med. 2015 Mar;43(3):721-8.
Kirk A. Campbell, M.D., Martin Quirno, M.D., Mathew Hamula, M.D., Hien Pham, M.D., Maxwell Weinberg, M.D., Fredrick J. Kummer, Ph.D., Laith M. Jazrawi, M.D., and Eric J. Strauss, M.D.
Kirk A. Campbell, M.D., Martin Quirno, M.D., Mathew Hamula, M.D., Hien Pham, M.D., Maxwell Weinberg, M.D., Fredrick J. Kummer, Ph.D., Laith M. Jazrawi, M.D., and Eric J. Strauss, M.D., Division of Sports Medicine, Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, New York, New York.
Correspondence: Kirk A. Campbell, M.D., Division of Sports Medicine, Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, 233 Broadway, 6th Floor, Suite 640, New York, New York 10279; email@example.com.
Caption: Figure 1 A, MTS set-up. B, Failure of intact specimen at the myotendinous junction. C, Failure of a repair at the tendon-bone-suture anchor interface. To view this figure in color, see www.hjdbulletin.org.
Table 1 Results Summary Control Group Load to failure N ([+ or -] SD) 501.8 ([+ or -] 145.3) Cycles to initial gap formation - (after 250 N load) (#) Initial displacement (mm) - Mean displacement (after cyclical loading) (mm) - Mode of failure MT junction Group 2 3S Load to failure N ([+ or -] SD) 284.7 ([+ or -] 43.4) Cycles to initial gap formation 0 (after 250 N load) (#) Initial displacement (mm) 3.29 Mean displacement (after cyclical loading) (mm) 10.3 Mode of failure TBS interface Group 3 5S Load to failure N ([+ or -] SD) 183.3 ([+ or -] 56.7) Cycles to initial gap formation 0 (after 250 N load) (#) Initial displacement (mm) 3.27 Mean displacement (after cyclical loading) (mm) 9.9 Mode of failure TBS interface Group 4 3L Load to failure N ([+ or -] SD) 502.4 ([+ or -] 100.6) Cycles to initial gap formation 58 (after 250 N load) (#) Initial displacement (mm) 0.6 Mean displacement (after cyclical loading) (mm) 5.7 Mode of failure 2 failed at TBS interface Group 5 5L Load to failure N ([+ or -] SD) 490.8 ([+ or -] 176.3) Cycles to initial gap formation 110 (after 250 N load) (#) Initial displacement (mm) 0.44 Mean displacement (after cyclical loading) (mm) 5.6 Mode of failure 1 failed at TBS interface 3S = 3 small suture anchors, 5S = 5 small suture anchors, 3L = 3 large suture anchors, 5L = 5 large suture anchors, TBS = tendon-bone-suture anchor. Table 2 Summary of Selected Clinical Outcomes Studies on Proximal Hamstring Repair with Suture Anchor Technique No. Patients Anchor No. Suture Anchors (No. Acutely Size and Repair Study Injured) (mm) Configuration Barnett et al., (21) 132 (38) 2.8 3 anchors Brucker and 8 (6) 2.9 Average 3.5 anchors Imhoff, (10) (range, 3-5 anchors) Chakravarthy et al., 2 (0/1) 3.5 1 (22) Cohen et al., (18) 52 (40) 3.0 5 "X" Cross et al., (3) 9 (0) Stay-Tec N/A Sutures Folsom and 21 (21) 2.9 2-3 anchors Larson, (11) Klingele and 11 (7) 2.9 2-3 anchors Sallay, (4) Konan and 10 (10) 2.9 3-5 anchors Haddad, (23) Wood et al., (7) 72 (32) 2.9 3 anchors Mean Follow-up Study (months) Outcomes Barnett et al., (21) 53.8 85% reported good or excellent result, 81% strength, and 106.4% endurance compared with contralateral side Brucker and 20 100% patient satisfaction, 88% torque Imhoff, (10) compared with contralateral side Chakravarthy et al., 12 All patients denied pain with ADLs (22) Cohen et al., (18) 33 91.4% with no pain, patients estimated strength recovery at [greater than or equal to] 75% Cross et al., (3) N/A Strength 60% of contralateral side Folsom and 20 96% patient satisfaction and 80% denied Larson, (11) pain, equivalent strength compared with contralateral Klingele and 34 91% patient satisfaction and 91% Sallay, (4) isokinetic strength compared with contralateral side Konan and 12 Return to sport within 6-9 months in Haddad, (23) 9/10 cases Wood et al., (7) 24 All improved outcome scores, better results if surgery within 3 months from injury