Purpose
The purpose of this study was to evaluate three different methods of attachment of continuous loop suspensory cortical preparation of all soft tissue central quad tendon grafts compared to a bone block control for anterior cruciate ligament reconstruction on construct displacement and load to failure.
Methods
Thirty-two cadaveric central quadriceps tendon (CQT) specimens were harvested, using three clinical techniques for graft fixation: cortical button alone (BTB EB), BTB cortical button with rip-stop suture (BTB RS), and continuous loop cortical button (BTB CL). A control group was also included that consisted of a bone block secured within testing clamps (BTB CON). Specimens were preloaded to 150 N. Tendons were then cyclically loaded between 50 N and 250 N for 1,000 cycles at .5 Hz. Displacement was measured at the point of fixation of the CQT after the 150 N preload, 250 N initial load and every 100th cycle. The specimens were loaded to failure after 1,000 cycles.
Results
There was a significant increase in displacement from .32 ± .56 mm for the BTB CON to 1.91 ± 1.13 mm for the BTB RS (P = .014) and 3.85 ± 2.32 mm for the BTB CL condition (P = .023). There was no significant increase in displacement for BTB EB (P = .182). Failure occurred for all of the BTB CL and 62.5% of the BTB EB specimens within the first 50 cycles. Twenty-five percent of the BTB CON specimens and 12.5% BTB RS failed at ∼400 and 500 cycles, respectively. Similar failure loads were observed for the BTB CON and the BTB RS (446.4 ± 151.46 N vs 505.74 ± 131.41 N; P = .99) Failure testing was not feasible for the BTB CL and BTB EB preparation methods.
Conclusion
In response to cyclic loading, the three all-soft tissue suspensory conditions experienced significantly greater displacement compared to the bone block controls. None of the soft-tissue conditions appeared superior when compared to each other.
Clinical Relevance
It remains unknown which method of soft-tissue suspensory provides optimal fixation. As these autografts become more common, it is essential to evaluate which fixation methods provide superior outcomes
Introduction
Central quadriceps tendon (CQT) autograft has been gaining popularity for anterior cruciate ligament (ACL) reconstruction. The reported rate of CQT as a graft choice for ACL reconstruction increased from 2.5% in 2010 to 11% in 2014.
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Anatomic anterior cruciate ligament reconstruction: A systematic review of surgical techniques and reporting of surgical data.
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Anatomic anterior cruciate ligament (ACL) reconstruction: A global perspective. Part 1.
In a recent publication from the ACL Study Group, surveying orthopaedic surgeons on their graft preferences, 13% responded that quad tendon was their secondary graft choice.
3- Sherman S.L.
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ACL Study Group presents the global trends in ACL reconstruction: Biennial survey of the ACL Study Group.
In addition, 33% and 10% predicted that bone-tendon-bone autograft and quad-tendon autograft will be the most commonly used grafts 10 years from now, respectively.
3- Sherman S.L.
- Calcei J.
- Ray T.
- et al.
ACL Study Group presents the global trends in ACL reconstruction: Biennial survey of the ACL Study Group.
This trend may be related to several factors such as hamstring tendon (HT) grafts having a higher rate of infection and a greater risk of rerupture.
4- Mariscalco M.W.
- Flanigan D.C.
- Mitchell J.
- et al.
The influence of hamstring autograft size on patient-reported outcomes and risk of revision after anterior cruciate ligament reconstruction: A Multicenter Orthopaedic Outcomes Network (MOON) Cohort Study.
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Functional outcome and graft retention in patients with septic arthritis after anterior cruciate ligament reconstruction: A systematic review.
CQT grafts are also larger and stronger than bone-patella tendon-bone (BPTB) grafts,
6- Shani R.H.
- Umpierez E.
- Nasert M.
- Hiza E.A.
- Xerogeanes J.
Biomechanical comparison of quadriceps and patellar tendon grafts in anterior cruciate ligament reconstruction.
and the CQT autograft has a low donor site morbidity profile compared to BPTB, while offering favorable anatomical and biomechanical properties.
7Quadriceps tendon graft for anterior cruciate ligament reconstruction: The graft of the future.
Biomechanical studies have shown that the CQT has a higher maximum tensile load (2,173–2,352 N),
6- Shani R.H.
- Umpierez E.
- Nasert M.
- Hiza E.A.
- Xerogeanes J.
Biomechanical comparison of quadriceps and patellar tendon grafts in anterior cruciate ligament reconstruction.
,8Graft selection in anterior cruciate ligament reconstruction.
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- Schatzmann L.
- Brunner P.
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Quadriceps tendon and patellar ligament: Cryosectional anatomy and structural properties in young adults.
compared to the BPTB graft (1,580 N) and native ACL (1,725–2,106 N).
6- Shani R.H.
- Umpierez E.
- Nasert M.
- Hiza E.A.
- Xerogeanes J.
Biomechanical comparison of quadriceps and patellar tendon grafts in anterior cruciate ligament reconstruction.
,10- Woo S.
- Hollis J.M.
- Adams D.J.
- Lyon R.M.
- Takai S.
Tensile properties of the human femur- anterior cruciate ligament-tibia complex The effects of specimen age and orientation.
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Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions.
Histologically, the CQT has 20% more collagen fibrils per cross-sectional area than the patellar tendon.
7Quadriceps tendon graft for anterior cruciate ligament reconstruction: The graft of the future.
Clinically, the CQT autograft has shown favorable results as a choice for ACL reconstruction while avoiding some of the postoperative complications associated with BPTB and HT autografts.
12- Fischer F.
- Fink C.
- Herbst E.
- et al.
Higher hamstring-to-quadriceps isokinetic strength ratio during the first post-operative months in patients with quadriceps tendon compared to hamstring tendon graft following ACL reconstruction.
,13- Lund B.
- Nielsen T.
- Faunø P.
- Christiansen S.E.
- Lind M.
Is quadriceps tendon a better graft choice than patellar tendon? A prospective randomized study.
A 2015 systematic review of 14 studies showed no difference between CQT graft reconstructions when compared to other graft choices with regard to arthrometric, Lachman, or pivot shift testing.
14- Slone H.S.
- Romine S.E.
- Premkumar A.
- Xerogeanes J.W.
Quadriceps tendon autograft for anterior cruciate ligament reconstruction: A comprehensive review of current literature and systematic review of clinical results.
Five of the 14 studies indicated less donor site morbidity, including anterior knee pain and patellar fracture, with CQT compared to BPTB. A 2014 prospective study comparing CQT to BPTB tendon grafts showed no significant difference in laxity as measured by KT-1000 at 2 years postoperation.
13- Lund B.
- Nielsen T.
- Faunø P.
- Christiansen S.E.
- Lind M.
Is quadriceps tendon a better graft choice than patellar tendon? A prospective randomized study.
Additionally, the CQT group had a significantly lower rate of pivot-shift compared to the BPTB group (14% vs 38%, respectively).
13- Lund B.
- Nielsen T.
- Faunø P.
- Christiansen S.E.
- Lind M.
Is quadriceps tendon a better graft choice than patellar tendon? A prospective randomized study.
This study also demonstrated lower rates of anterior knee pain for CQT patients (7%) compared to BTB patients (34%). When compared to HT grafts, the CQT grafts preserves the function of the hamstrings, which serve as an ACL agonist, suggesting that CQT harvest results in a protective hamstring to quadriceps muscle strength ratio, which may result in lower stress rates on the ACL.
12- Fischer F.
- Fink C.
- Herbst E.
- et al.
Higher hamstring-to-quadriceps isokinetic strength ratio during the first post-operative months in patients with quadriceps tendon compared to hamstring tendon graft following ACL reconstruction.
Multiple techniques have been described for the harvest and fixation of CQT for ACL reconstruction.
15- Lippe J.
- Armstrong A.
- Fulkerson J.P.
Anatomic guidelines for harvesting a quadriceps free tendon autograft for anterior cruciate ligament reconstruction.
, 16- Fink C.
- Herbort M.
- Abermann E.
- Hoser C.
Minimally invasive harvest of a quadriceps tendon graft with or without a bone block.
, 17- Slone H.S.
- Ashford W.B.
- Xerogeanes J.W.
Minimally invasive quadriceps tendon harvest and graft preparation for all-inside anterior cruciate ligament reconstruction.
, 18- Sheean A.J.
- Musahl V.
- Slone H.S.
- et al.
Quadriceps tendon autograft for arthroscopic knee ligament reconstruction: Use it now, use it often.
, 19- Fulkerson J.P.
- McKeon B.P.
- Donahue B.J.
- Tarinelli D.J.
The central quadriceps tendon as a versatile graft alternative in anterior cruciate ligament reconstruction: Techniques and observations.
, 20Anterior cruciate ligament (ACL) reconstruction with quadriceps tendon autograft and press-fit fixation using an anteromedial portal technique.
, 21- DeAngelis J.P.
- Fulkerson J.P.
Quadriceps tendon—a reliable alternative for reconstruction of the anterior cruciate ligament.itle.
Techniques include full and partial thickness tendon harvest, both with and without the harvest of a bone block from the superior pole of the patella. The use of a bone block has the advantage of bony healing within the tunnel.
22- Tomita F.
- Yasuda K.
- Mikami S.
- Sakai T.
- Yamazaki S.
- Tohyama H.
Comparisons of intraosseous graft healing between the doubled flexor tendon graft and the bone-patellar tendon-bone graft in anterior cruciate ligament reconstruction.
All soft tissue grafts have the advantage of a smaller incision and decreased anterior knee pain, and they remove the risk of potential patella fracture.
7Quadriceps tendon graft for anterior cruciate ligament reconstruction: The graft of the future.
However, soft tissue-based CQT grafts rely on the strength of the graft preparation technique, often using high-strength sutures with or without a suspensory fixation device, which is often the weak point in the construct that may contribute to failure
18- Sheean A.J.
- Musahl V.
- Slone H.S.
- et al.
Quadriceps tendon autograft for arthroscopic knee ligament reconstruction: Use it now, use it often.
,23- Michel P.A.
- Domnick C.
- Raschke M.J.
- et al.
Soft tissue fixation strategies of human quadriceps tendon grafts: A biomechanical study.
These factors have created controversy as to what is the optimal fixation method for CQT autografts.
The purpose of this study was to evaluate three different clinical methods of attachment of continuous loop suspensory cortical preparation of all soft tissue CQT grafts for ACL reconstruction on construct displacement and load to failure. We hypothesised that the addition of a rip-stop suture to a BTB Endobutton (Smith and Nephew, Inc., Andover, MA) passed through the soft tissue graft would provide similar cyclic and load to failure characteristics to a graft remaining attached to a patellar bone block.
Discussion
The main finding of this study is that each of the all soft tissue suspensory preparation methods experienced significantly greater displacement with preload and cyclic loading compared to the BTB CON. Early failure was noted for the majority of specimens in the BTB CL and BTB EB groups during cyclic testing, while six of the BTB CON and all of the BTB RS groups completed the cyclic testing without complete tissue failure and were available for the failure testing. While the load-to-failure of the BTB RS was similar to that of the BTB CON, the all soft tissue preparation had already experienced significant displacement (>3 mm) that was representative of clinical failure.
25- Eguchi A.
- Ochi M.
- Adachi N.
- Deie M.
- Nakamae A.
- Usman M.A.
Mechanical properties of suspensory fixation devices for anterior cruciate ligament reconstruction: Comparison of the fixed-length loop device versus the adjustable-length loop device.
Importantly, all of the BTB CL group failed early in the cyclic testing (failure at the tissue flap), while only 37.5% of the BTB EB group completed the cyclic loading, with all failures involving the loop pulling through the tissue. Although the addition of the rip-stop improved the construct strength, all of the failures of the BTB RS involved the suture constricting the tissue and pulling the loop through the center of the tendon.
Methods for securing all soft tissue quadriceps grafts have been previously studied.
23- Michel P.A.
- Domnick C.
- Raschke M.J.
- et al.
Soft tissue fixation strategies of human quadriceps tendon grafts: A biomechanical study.
,28- Hahn J.M.
- Inceoʇlu S.
- Wongworawat M.D.
Biomechanical comparison of Krackow locking stitch versus nonlocking loop stitch with varying number of throws.
Michel et al. investigated suture type (doubled no. 2 vs single no. 5 composite suture) and stitch type (Krackow, whip and baseball), on cyclic and load-to-failure.
23- Michel P.A.
- Domnick C.
- Raschke M.J.
- et al.
Soft tissue fixation strategies of human quadriceps tendon grafts: A biomechanical study.
The Krackow stitch with a doubled no. 2 suture was shown to have the most favorable characteristics; however, the magnitude of displacement (10.59 ± −2.63 mm) in response to cyclic loading was significantly greater than what we observed with the BTB RS and bone block CQT in our study. In a similar study, Hahn et al. compared Krackow and baseball stitches in porcine flexor tendons.
28- Hahn J.M.
- Inceoʇlu S.
- Wongworawat M.D.
Biomechanical comparison of Krackow locking stitch versus nonlocking loop stitch with varying number of throws.
They also found a significantly greater displacement (15 ± −4 mm) with the Krackow stich, which again is greater than the displacements that we observed in our study. The difference between these studies and ours may be due to our testing protocol. We adjusted our cyclic loading data with respect to the displacements that occurred following the preloading stages of testing. This represents the clinical scenario in which the prepared graft is preloaded on the back table to remove suture creep prior to inserting the graft into the knee. We also hypothesized that the use of the continuous loop device would reduce the amount of displacement in the construct, by removing the issue of suture creep within the soft tissue graft, as is observed with the more traditional Krakow and whip suture configurations. Furthermore, the weak link in soft tissue suture application is often the method of fixation of the suture to bone. Sutures tied over a cortical button or screw post have the potential for knot slippage and loss of graft fixation.
29- Cole B.J.
- Sayegh E.T.
- Yanke A.B.
- Chalmers P.N.
- Frank R.M.
Fixation of soft tissue to bone: Techniques and fundamentals.
Continuous loop cortical suspensory fixation devices, such as the Endobutton CL (Smith and Nephew, Inc.), have been shown to provide the strongest fixation properties for soft tissue grafts.
25- Eguchi A.
- Ochi M.
- Adachi N.
- Deie M.
- Nakamae A.
- Usman M.A.
Mechanical properties of suspensory fixation devices for anterior cruciate ligament reconstruction: Comparison of the fixed-length loop device versus the adjustable-length loop device.
,26- Petre B.M.
- Smith S.D.
- Jansson K.S.
- et al.
Femoral cortical suspension devices for soft tissue anterior cruciate ligament reconstruction: A comparative biomechanical study.
Our soft tissue displacements are consistent with those reported in studies by Sakaguchi et al.
30- Sakaguchi K.
- Tachibana Y.
- Oda H.
Biomechanical properties of porcine flexor tendon fixation with varying throws and stitch methods.
and Eguchi et al.
25- Eguchi A.
- Ochi M.
- Adachi N.
- Deie M.
- Nakamae A.
- Usman M.A.
Mechanical properties of suspensory fixation devices for anterior cruciate ligament reconstruction: Comparison of the fixed-length loop device versus the adjustable-length loop device.
in both magnitude and pattern. In these studies, there was an abrupt increase in displacement between 0 and 200 cycles followed by a slow leveling out to 1,000 cycles.
25- Eguchi A.
- Ochi M.
- Adachi N.
- Deie M.
- Nakamae A.
- Usman M.A.
Mechanical properties of suspensory fixation devices for anterior cruciate ligament reconstruction: Comparison of the fixed-length loop device versus the adjustable-length loop device.
,30- Sakaguchi K.
- Tachibana Y.
- Oda H.
Biomechanical properties of porcine flexor tendon fixation with varying throws and stitch methods.
With respect to load to failure, Eguchi et al. compared soft tissue fixation of fixed loop versus adjustable loop devices.
25- Eguchi A.
- Ochi M.
- Adachi N.
- Deie M.
- Nakamae A.
- Usman M.A.
Mechanical properties of suspensory fixation devices for anterior cruciate ligament reconstruction: Comparison of the fixed-length loop device versus the adjustable-length loop device.
The fixed loop (Endobutton CL) failed at approximately 1,100 N compared to 870 N with the adjustable loop (Tightrope), with the majority of failures attributed to tendon rupture (Endobutton) and broken loops (Tightrope). Two other studies determined that the displacement or slippage of hamstring grafts was approximately .6 mm to 3 mm depending on the type of fixation that was used.
31A comparison of five tibial-fixation systems in hamstring-graft anterior cruciate ligament reconstruction.
,32- Giurea M.
- Zorilla P.
- Amis A.A.
- Aichroth P.
Comparative pull-out and cyclic-loading strength tests of anchorage of hamstring tendon grafts in anterior cruciate ligament reconstruction.
Both of these studies used screws, washers, and anchors as their mode of fixation, which are mechanically different than the suspensory fixation devices that were tested in our study.
A previous study comparing CQT and BTB grafts observed load to failure to be 2,189 N and 1,580 N, respectively.
6- Shani R.H.
- Umpierez E.
- Nasert M.
- Hiza E.A.
- Xerogeanes J.
Biomechanical comparison of quadriceps and patellar tendon grafts in anterior cruciate ligament reconstruction.
These failure loads are larger than those reported in our study, with the differences potentially being attributed to the different experimental setups. For example, in the current study a partial thickness CQT graft used compared to the full-thickness graft used in the previous study. In addition, Shani et al. cemented their bone blocks while our BTB CON were secured with mechanical clamps.
6- Shani R.H.
- Umpierez E.
- Nasert M.
- Hiza E.A.
- Xerogeanes J.
Biomechanical comparison of quadriceps and patellar tendon grafts in anterior cruciate ligament reconstruction.
Although the pressure exerted by the clamps used in this investigation may be indicative of the pressure exerted by an interference screw, fixation of the bone blocks should not be interpreted clinically and was included to serve only as a control group. While using a fixation screw would better replicate the clinical scenario, we opted to use the mechanical grips to reduce the variability that would have been introduced by incorporating interreference screws. The loads to failure reported in our study fall within a range of those for four-strand hamstring tendon grafts reported to be from 445 N to 2,421 N depending on the type of fixation used,
31A comparison of five tibial-fixation systems in hamstring-graft anterior cruciate ligament reconstruction.
, 32- Giurea M.
- Zorilla P.
- Amis A.A.
- Aichroth P.
Comparative pull-out and cyclic-loading strength tests of anchorage of hamstring tendon grafts in anterior cruciate ligament reconstruction.
, 33- Wilson T.W.
- Zafuta M.P.
- Zobitz M.
A biomechanical analysis of matched bone-patellar tendon-bone and double-looped semitendinosus and gracilis tendon grafts.
Finally, our results also agree favorably with a study that noted a failure load of 606.3 N when an interference screw was used for tibial side fixation.
34- Karkosch R.F.
- Ettinger M.
- Bachmaier S.
- Wijdicks C.A.
- Smith T.
Adjustable-length loop cortical button versus interference screw fixation in quadriceps tendon anterior cruciate ligament reconstruction—A biomechanical in vitro study.
When compared to the BTB CON specimens, the BTB RS had the same load to failure but displayed significantly greater tendon displacement at all cycles. It should be reiterated that two of the BTB CON specimens and one of the BTB RS specimens failed at ∼400 and 500 cycles, respectively. However, it has been suggested that displacements greater than 3 mm represent a clinical failure of the fixation, as this inhibits graft healing.
25- Eguchi A.
- Ochi M.
- Adachi N.
- Deie M.
- Nakamae A.
- Usman M.A.
Mechanical properties of suspensory fixation devices for anterior cruciate ligament reconstruction: Comparison of the fixed-length loop device versus the adjustable-length loop device.
Even if bone-tendon healing still takes place, the progressive displacement may lead to decreased postoperative stability and failure of the reconstruction. Applying this failure criteria to the current study, all of the BTB RS would have failed between 200 and 300 cycles after accounting for the displacements incurred from the preload.
While caution must be used when interpreting the BTB CON results in comparison to the clinical environment using an interference screw, the results do suggest that fixation may be improved using a bone block. Although the BTB CON specimens exhibited significantly less displacement in response to the cyclic loading, this must be balanced with the risks associated with bone block harvesting, such as postoperative anterior knee pain or patella fracture.
35- Lee S.
- Sang C.S.
- Jo C.H.
- Hyuk S.H.
- Joon H.A.
- Myung C.L.
Anterior cruciate ligament reconstruction with use of autologous quadriceps tendon graft.
, 36- Fu F.H.
- Rabuck S.J.
- West R.V.
- Tashman S.
- Irrgang J.J.
Patellar fractures after the harvest of a quadriceps tendon autograft with a bone block: A case series.
, 37- Ferrer G.A.
- Miller R.M.
- Murawski C.D.
- et al.
Quantitative analysis of the patella following the harvest of a quadriceps tendon autograft with a bone block.
Fu et al. examined a series of 57 patients that underwent CQT harvest with bone block and found an incidence of 3.5% intraoperative patella fracture and 8.8% at 2 years follow-up; some of these fractures were only seen on computed tomography scan and, thus, may not be clinically relevant.
36- Fu F.H.
- Rabuck S.J.
- West R.V.
- Tashman S.
- Irrgang J.J.
Patellar fractures after the harvest of a quadriceps tendon autograft with a bone block: A case series.
After reviewing the fracture cases and imaging, the authors suggested that the risk of fracture was multifactorial and included eccentric harvest site (more lateral), harvesting >50% of anteroposterior thickness, harvesting >50% of mediolateral width, failure of bone graft incorporation, and stress risers at the corner of harvest site. Patellae that have less than 27% of their thickness harvested for a bone block are also less likely to fracture than those that have 42% of their thickness harvested.
37- Ferrer G.A.
- Miller R.M.
- Murawski C.D.
- et al.
Quantitative analysis of the patella following the harvest of a quadriceps tendon autograft with a bone block.
With appropriate harvesting technique and patient selection, the risk of patella fracture can be minimized, thus making CQT with bone plug potentially a safer and more stable graft choice.
Limitations
Limitations in this study include the small sample size for each testing group and the relatively older age of the specimens. Despite the small sample, effect sizes were large, and the post hoc power analysis indicated that it was adequately powered. Additionally, early failure during cyclic testing further reduced sample size and may limit the applicability of load-to-failure testing. With respect to the testing methodology, the line of pull in the current study does not necessarily reflect the physiological stresses placed on the grafts in a human knee. Previous studies have shown higher loads to failure in physiological stresses compared to a straight line of pull.
10- Woo S.
- Hollis J.M.
- Adams D.J.
- Lyon R.M.
- Takai S.
Tensile properties of the human femur- anterior cruciate ligament-tibia complex The effects of specimen age and orientation.
,11- Noyes F.R.
- Butler D.L.
- Grood E.S.
- Zernicke R.F.
- Hefzy M.S.
Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions.
Changing the orientation may have an effect on cyclic loading and rate of displacement. Our study also did not incorporate tibia-sided fixation. Although this could have altered graft behavior, this was outside of the scope of our study, as we were examining the difference in femur-sided suspensory fixation devices. Additionally, tibia-sided fixation would have been standard in all four groups and, thus, would not have added any additional between-group changes. Finally, it is difficult to interpret what the displacement in this biomechanical model would translate to in vivo and if this would create symptomatic laxity. The threshold for failure and revision surgery in the context of ACL reconstruction is generally regarded as persistent symptomatic laxity.
Conclusion
The bone block controls experienced significantly less displacement when compared to the 3 all-soft tissue fixation suspensory devices. However, the BTH RS specimens failed at similar forces compared to the BTB CON group.
Article info
Publication history
Published online: March 25, 2022
Accepted:
December 1,
2021
Received:
April 22,
2021
Footnotes
This research was funded by Smith and Nephew Inc. (A17-ASDUS-GR-598).
The authors report the following potential conflicts of interest or sources of funding: T.A.B. reports grants from Smith and Nephew, during the conduct of the study. A.G. reports grants from Smith and Nephew, during the conduct of the study; grants and personal fees from Smith and Nephew, grants from Ossur, personal fees from Precision OS and personal fees from Xiros Ltd, outside the submitted work. Full ICMJE author disclosure forms are available for this article online, as supplementary material.
Copyright
© 2022 The Authors. Published by Elsevier Inc. on behalf of the Arthroscopy Association of North America