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n Feature Article Biomechanical Study of a Subscapularis Repair Technique for Total Shoulder Arthroplasty Evan Lederman, MD; Jonathan Streit, MD; John Idoine, DO; Yousef Shishani, MD; Reuben Gobezie, MD abstract Secure subscapularis repair is an essential element of total shoulder arthroplasty. Some surgeons prefer subscapularis peel because of ease of use, but some evidence suggests that lesser tuberosity osteotomy provides better fixation. The authors developed a novel, through-implant repair technique and performed a biomechanical study of its strength with cadaveric specimens. The authors obtained 20 matched pairs of cadaveric shoulders and inserted an uncemented short-stemmed humeral prosthesis that facilitates throughimplant repair in all specimens. For each cadaver, the subscapularis was repaired with lesser tuberosity osteotomy and standard suture technique on 1 side, and the contralateral subscapularis was repaired with a novel throughimplant suture repair and subscapularis peel technique. Displacement of the subscapularis footprint, ultimate load to failure, and stiffness of each repair were measured and compared between fixation groups. Mean±SD displacement of the lesser tuberosity osteotomy group was 0.75±0.94 mm at 10 cycles and 2.24±2.76 mm at 500 cycles. Mean±SD load to failure was 612±185 N, and mean±SD ultimate stiffness was 119±32 N/mm. No significant differences were noted between the lesser tuberosity osteotomy group and the subscapularis peel group in mean±SD displacement at 10 cycles (1.09±1.30 mm, P=.31), mean±SD displacement at 500 cycles (2.85±2.43 mm, P=.26), mean±SD load to failure (683±274 N, P=.31), or mean±SD ultimate stiffness (117±37 N/mm, P=.88). In a biomechanical testing model, through-implant subscapularis repair provided secure fixation relative to currently accepted subscapularis repair techniques in total shoulder replacement. [Orthopedics. 2016; 39(5):e937-e943.] T otal shoulder arthroplasty (TSA) is an effective treatment for glenohumeral joint arthritis in the setting of an intact rotator cuff. Current techniques for TSA using the deltopectoral approach necessitate detachment of the subscapularis tendon from the humerus for placement of the prosthesis. This may be accom- SEPTEMBER/OCTOBER 2016 | Volume 39 • Number 5 plished by tenotomizing the subscapularis tendon, peeling the tendon insertion away from the lesser tuberosity, or performing an osteotomy of the lesser tuberosity, with refixation of the tendon insertion after the procedure. Most surgeons restrict shoulder motion in the postoperative period to allow healing of the subscapularis repair. Despite this period of rest, several clinical studies showed that partial or complete failure of the repair is common and likely negatively affects the final outcome.1,2 The authors are from The Orthopedic Clinic Association and University of Arizona (EL), College of Medicine, Phoenix, Arizona; University Hospitals Case Medical Center (JS), Cleveland, Ohio; and the Cleveland Shoulder Institute (JI, YS, RG), Beachwood, Ohio. Drs Shishani and Gobezie are previous Blue Ribbon Article Award recipients (Orthopedics, July/August 2016). Drs Streit, Idoine, and Shishani have no relevant financial relationships to disclose. Dr Lederman is a paid consultant for and receives grants and royalties from Arthrex Inc. Dr Gobezie is a paid consultant for and receives grants and royalties from Arthrex Inc. Correspondence should be addressed to: Reuben Gobezie, MD, Cleveland Shoulder Institute, 3999 Richmond Rd, Ste 200, Beachwood, OH 44122 ([email protected]). Received: May 6, 2015; Accepted: September 23, 2015. doi: 10.3928/01477447-20160623-09 e937 n Feature Article scapularis tenotomy, subscapularis peel, or lesser tuberosity osteotomy to gain access to the glenohumeral joint. The authors’ preferred technique is to perform a subscapularis peel that involves removal of the entire tendon from its footprint on the lesser tuberosity. Once the subscapularis is released, the glenohumeral joint can be disarticulated to deliver the proximal humerus into the surgical field. Any osteophytes that distort the native anatomy are removed with a rongeur. Preparation of the humerus begins with an anatomic neck cut. A sound is used to identify the humeral canal, followed by reaming and broaching until a snug fit without toggle is achieved. The size of the final broach corresponds to the size of the final humeral implant. Figure 1: The prosthesis is loaded with 6 nonabsorbable sutures, for a total of 12 suture strands to be tied. Figure 2: Before implantation, 2 holes are drilled in the bicipital groove to receive the 2 sutures that were initially passed through the lateral fin on the prosthesis. Figure 3: The implant is impacted into the humeral canal, with care taken to maintain tension on the medial suture strands so that they retain their order. Several biomechanical studies have been performed in an attempt to determine the strongest method of subscapularis fixation after TSA. Despite a lack of consensus in the literature,1,3-10 lesser tuberosity osteotomy is considered to provide the most secure construct over the long term because it relies on osseous healing and does not compromise the tendon insertion site and footprint. However, subscapularis tenotomy and subscapularis peel procedures take less surgical time and avoid the possibility of tuberosity nonunion.2 e938 Regardless of technique, many surgeons perform subscapularis repair by passing heavy nonabsorbable suture around the humeral prosthesis. The authors developed a novel TSA design and repair technique for the subscapularis that uses the prosthesis as an anchoring device. The authors performed a cadaveric study of the strength of the repair, and this report describes the technique and the results of a biomechanical study of an uncemented humeral prosthesis that allows subscapularis repair with multiple sutures that are passed through the device. Materials and Methods Approach and Humeral Preparation Total shoulder arthroplasty with a suture-incorporating prosthesis is performed with the patient in the beach chair position. A standard deltopectoral approach to the shoulder is used to provide exposure of the subscapularis and rotator interval. The surgeon may perform sub- Through-implant Subscapularis Suture Repair After broaching, the final humeral prosthesis is ready to be inserted. On the back table, the prosthesis is loaded with 6 nonabsorbable sutures, for a total of 12 suture strands to be tied (Figure 1). The first 2 sutures are passed through the lateral fin of the implant; the superior suture is blue, and the inferior suture is tiger striped. The remaining 4 sutures are passed through specially designed suture holes along the medial edge of the implant. It is important to alternate the suture color to facilitate knot tying later in the case. Before implantation, 2 holes are drilled in the bicipital groove to receive the 2 sutures that were initially passed through the lateral fin on the prosthesis (Figure 2). The authors use the prosthesis itself as a guide for the location of these holes and pass the sutures with a suture passer. The implant is then impacted into the humeral canal, with care taken to maintain tension on the medial suture strands so that they retain their order (Figure 3). With the implant seated, the 8 medial suture strands are passed through the subscapularis tendon in a uniform fashion (Figure 4). The authors’ preferred method is to pass Copyright © SLACK Incorporated n Feature Article Figure 4: With the implant seated, the 8 medial suture strands are passed through the subscapularis tendon in a uniform fashion. the suture with an Arthrex FastPass Scorpion suture passer (Arthrex, Inc, Naples, Florida), but free needles also can be used. Suture Configuration The knot tying sequence follows a specific pattern, as shown in Figure 5. No sutures are tied to themselves, and each strand is tied to a different strand in the configuration. Therefore, the sutureimplant complex does not become taut until the final 2 knots are tied. Knot tying is facilitated by the placement of suture strands in the prosthesis so that strands of the same color are tied together, as shown in Figure 5A. The tying sequence begins by tying the superiormost strand of the medial 8 strands (blue) to 1 of the superior strands from the lateral fin (also blue), as shown in Figure 5B. Next the inferiormost strand of the medial 7 strands (tiger stripe) is tied to 1 of the inferior strands from the lateral fin (also tiger stripe), as shown in Figure 5C. Next the remaining inferior suture from the lateral fin (tiger stripe) is tied to the third strand from the top of Figure 5: Initial layout of the 12 strings of sutures (A). Superior knot tying (B). Inferior knot tying (C). First lateral to medial knot tying (D). Second lateral to medial knot tying (E). Medial row knot tying and final knot configuration (F). the remaining 6 medial strands (also tiger stripe), as shown in Figure 5D. Then the final superior suture from the lateral fin (blue) is tied to the third strand from the SEPTEMBER/OCTOBER 2016 | Volume 39 • Number 5 bottom of the remaining 5 medial strands (also blue), as shown in Figure 5E. Finally, the top 2 and bottom 2 medial strands are tensioned to tighten the construct and e939 n Feature Article Figure 7: Comparison of cyclic displacement of the subscapularis tendon from bone after 10 cycles and 500 cycles showed no difference between lesser tuberosity osteotomy with standard suture configuration and subscapularis peel with a sutureincorporating humeral prosthesis. Figure 6: The final subscapularis repair should have secure knots that are evenly spaced about the tendon footprint. Figure 9: Comparison of construct stiffness showed no difference between lesser tuberosity osteotomy with standard suture configuration and subscapularis peel with a suture-incorporating humeral prosthesis. Figure 8: Comparison of ultimate load to failure showed no difference between lesser tuberosity osteotomy with standard suture configuration and subscapularis peel with a suture-incorporating humeral prosthesis. then they are tied together. These final 2 knots break the rule of matching suture colors, as shown in Figure 5F. The final construct should have secure knots that are evenly spaced about the tendon footprint (Figure 6). Cadaveric Study To test the strength of subscapularis repair performed with a throughimplant technique, the authors obtained 20 matched pairs of fresh frozen cadaveric e940 shoulders with overlying soft tissues removed, an intact rotator cuff, and a potted humerus. Cadavers were all male, with a mean±SD age of 58.1±10.6 years and no previous shoulder injury or surgery. An uncemented short-stemmed humeral prosthesis that facilitates through-implant repair (Univers Apex; Arthrex) was implanted in all specimens. Cadavers were prospectively randomized to side (right vs left) and surgical technique (lesser tuberosity osteotomy vs subscapularis peel). For each cadaver, the subscapularis was repaired with a lesser tuberosity osteotomy with standard suture technique10 on 1 side, whereas the contralateral subscapularis was repaired with a novel through-implant suture repair and subscapularis peel technique. Specimens that received lesser tuberosity osteotomy repair constituted the control group, and those that received the subscapularis peel technique and through-implant su- ture repair constituted the experimental group. Lesser tuberosity osteotomy repairs were made with 4 No. 5 FiberWire sutures (Arthrex) that were passed through bone tunnels in the lateral bicipital groove and around the humeral stem before implantation. The free suture tail was then passed through the tendon with a modified MasonAllen stitch and tied over the lesser tuberosity osteotomy.11 The same technique as described earlier was used for all throughimplant subscapularis suture repairs in the experimental group. Using a hydraulic testing system (Instron, Canton, Massachusetts), each specimen was cycled at 10 to 100 N for 500 cycles and then pulled to failure at 33 mm/s. Displacement of the subscapularis footprint was measured from its original position after 10 cycles and again after 500 cycles. Ultimate load to failure of each construct was quantified, and the mechanism of failure was documented. The stiffness of each construct was calculated as force/displacement at the bone-tendon junction. Statistical analysis was performed with Student’s t test to compare mean and SD, with significance set at alpha=0.05. Results Mean±SD displacement for the control group was 0.75±0.94 mm at 10 cycles and 2.24±2.76 mm at 500 cycles (Figure 7). Mean±SD load to failure was 612±185 N, and mean±SD ultimate stiffness was 119±32 N/mm. No significant differences were found between the control group and the experimental group in mean±SD displacement at 10 cycles (1.09±1.30 mm, P=.31), mean±SD displacement at 500 cycles (2.85±2.43 mm, P=.26), mean±SD load to failure (683±274 N, P=.31), or mean±SD ultimate stiffness (117±37 N/ mm, P=.88) (Figures 8-9). Individual data, including mode of failure, are shown in Table 1 and Table 2. Discussion Failure of subscapularis repair negatively affects subjective and objective Copyright © SLACK Incorporated n Feature Article Table 1 Displacement, Load to Failure, Stiffness, and Failure Mode Data for the Control Group Specimen Displacement at 10 Cycles, mm Displacement at 500 Cycles, mm Ultimate Load, N Stiffness, N/mm Failure Mode C120430L 0.19 0.96 586.49 179.47 Bone fractured, implant pulled out C121212R 1.00 2.67 649.88 81.42 Suture tore through tendon C131040R 0.27 0.63 495.00 100.15 Bone fractured, implant pulled out C131344L 0.40 0.69 450.57 84.28 Suture broke C131420R 0.57 2.16 216.15 105.87 Knot failure L130716R 1.36 Not applicable 832.24 111.38 Suture broke, knot failure S131778R 0.31 0.63 663.67 213.34 Bone fractured, implant pulled out C121966L 0.23 1.11 703.77 109.55 Bone fractured, implant pulled out S120195R 0.54 1.98 606.97 132.44 Knot failure, bone fractured, implant pulled out S120757R 0.34 1.32 666.91 118.42 Knot failure, suture slipped under implant S121187R 0.64 1.95 917.21 121.61 Knot failure, bone fractured, implant pulled out S121660R 0.89 2.68 467.25 135.53 Knot failure, bone fractured, implant pulled out F130694R 0.21 0.58 958.44 116.45 Knot failure, implant pulled out F140040R 0.59 3.21 835.95 87.89 Knot failure, implant pulled out F140131L 0.97 1.30 510.85 107.96 Implant pulled out F140134L 0.98 3.72 324.06 95.88 Knot failure, bone fractured, implant pulled out F140214L 0.22 0.44 677.52 116.83 Knot failure, implant pulled out F140303L 0.53 3.08 559.36 85.98 Knot failure, suture slipped under implant C140351L 4.50 12.82 542.38 126.18 Knot failure, bone fractured, implant pulled out C140403L 0.22 0.64 584.91 144.30 Knot failure, bone fractured, implant pulled out Mean 0.75 2.24 612 119 SD 0.94 2.76 185 32 results after TSA. Liem et al9 performed tenotomy with transosseous repair and showed partial repair defects in 30% of patients with ultrasound at a mean followup of 43 months. In addition, 25% of their study cohort showed both subjective and objective signs of diminished function. Miller et al12 reported that subscapularis rupture after TSA results in delayed rehabilitation and a possible need for additional surgery and produces inferior outcomes, even with adequate treatment. Use of the humeral prosthesis as an anchoring device is a novel approach. The current biomechanical study showed that subscapularis repair through a humeral prosthesis specifically designed for subscapularis repair options allows subscapularis peel repair to achieve equivalent strength to lesser tuberosity osteotomy. This study used subscapularis peel and lesser tuberosity osteotomy as fixation techniques in biomechanical testing. If suture incorporation through the humeral prosthesis could be shown to make subscapularis peel as strong as the current gold standard of lesser tuberosity osteotomy with a nonincorporating device, this would theoretically provide equivalent potential for healing with a simplified surgical technique. Despite the theoretical advantage of osseous healing after lesser tuberosity osteotomy, the results of biomechanical and clinical studies comparing the techniques have been mixed. Fishman et al3 found more gapping at the repair site SEPTEMBER/OCTOBER 2016 | Volume 39 • Number 5 with cyclic loading with the use of tenotomy rather than lesser tuberosity osteotomy to access the glenohumeral joint, with equivalent load to failure. Krishnan et al7 observed superior load to failure with lesser tuberosity osteotomy compared with tenotomy. Jandhyala et al6 showed superior strength to belly press testing in patients who underwent lesser tuberosity osteotomy compared with those who underwent tenotomy during TSA. Giuseffi et al4 found that tenotomy produced less displacement to cyclic loading and equivalent load to failure compared with lesser tuberosity osteotomy. Other authors8,13 found no clear superiority of 1 technique. Subscapularis peel and tenotomy are simple techniques that are favored by e941 n Feature Article Table 2 Displacement, Load to Failure, Stiffness, and Failure Mode Data for the Experimental Group Specimen Displacement at 10 Cycles, mm Displacement at 500 Cycles, mm Ultimate Load, N Stiffness, N/mm Failure Mode C120430R 0.68 1.97 894.54 136.01 Suture broke, knot failure C121212L 0.42 1.93 493.40 81.66 Suture broke C131040L 0.60 1.97 595.94 141.99 Suture tore through tendon, knot failure C131344R 0.13 0.23 1388.44 168.81 Suture broke C131420L 0.36 1.64 441.48 79.19 Suture tore through tendon, knot failure L130716L 0.38 1.54 1105.96 116.71 Suture tore through tendon, knot failure S131778L 0.35 1.39 475.52 98.76 Bone fractured, implant pulled out C121966R 0.27 0.37 1010.38 62.36 Suture tore through tendon S120195L 1.32 4.23 420.84 129.79 Suture broke, implant pulled out S120757L 1.49 2.90 1064.80 134.17 Knot failure, implant pulled out S121187L 0.76 1.95 646.26 141.25 Suture broke, implant pulled out S121660L 1.06 2.90 672.94 160.69 Knot failure, implant pulled out F130694L 1.25 3.18 530.75 133.53 Suture broke, implant pulled out F140040L 0.16 1.28 731.98 124.85 Suture broke, implant pulled out F140131R 0.71 2.06 425.73 99.51 Knot failure, suture broke, implant pulled out F140134R 4.94 10.08 438.38 90.38 Knot failure, implant pulled out F140214R 0.50 1.84 741.99 84.55 Knot failure, implant pulled out F140303R 4.38 7.21 582.04 84.56 Suture broke, implant pulled out C140351R 1.54 6.39 490.56 70.96 Bone fractured, implant pulled out C140403R 0.46 1.97 505.30 204.37 Suture broke, implant pulled out Mean 1.09 2.85 683 117 SD 1.30 2.43 274 37 many surgeons for their ease of use and because they avoid the possibility of lesser tuberosity nonunion that may occur after lesser tuberosity osteotomy.2 In older patients, the subscapularis tendon insertion may have degeneration or partial tears. In patients with surgery involving the subscapularis tendon, the insertion may have been lateralized or compromised. This may affect the ability to perform lesser tuberosity osteotomy or tenotomy, and peeloff can preserve maximal tendon length and allow for repair of the tendon to the lesser tuberosity. The authors prefer to use subscapularis peel and have found that it produces excellent results. However, Ahmad et al1 showed that this technique alters the anatomy of the subscapularis e942 insertion, compromising the strength of repair. Subscapularis repair with the use of the humeral prosthesis as an anchoring device does not produce a more anatomic fixation, but it appears to provide better initial strength during the healing period. The technique, as designed, allows for dynamic equalization of tension across the suture construct by the nature of the sliding suture holes and the practice of tying each suture strand to a strand from another suture. This attribute is unique to this technique and the use of this specifically designed device. The authors use this device because it provides superior initial fixation strength and also may reduce the risk of tuberosity fracture with subscapularis peel. The superior initial fixation provided by incorporating sutures through the humeral prosthesis may reduce the incidence of lesser tuberosity nonunion when lesser tuberosity osteotomy is used, but further clinical studies with advanced imaging techniques are needed to determine whether this benefit exists. Avoiding the devastating complication of subscapularis failure will improve patient outcomes and reduce revision rates. Limitations Limitations of the study include its short-term nature. Biomechanical studies and short-term clinical outcome studies do not provide information on the ultimate healing potential of this construct. However, this study was conducted simi- Copyright © SLACK Incorporated n Feature Article larly to other studies of subscapularis repair.4,7,10,13 Further clinical study of the suture-incorporating humeral prosthesis is needed to determine whether it offers a true benefit in terms of shorter operative time and improved patient outcomes. Conclusion The results of this biomechanical study show that a through-implant suture technique allows subscapularis peel to achieve similar strength to lesser tuberosity osteotomy in terms of displacement to cyclic loading, ultimate load to failure, and stiffness. The authors have begun to use this device in clinical practice and are monitoring the early outcomes of patients treated with the device to determine whether there is a true clinical benefit when the subscapularis is fixed with a throughimplant suturing technique. References 1. Ahmad CS, Wing D, Gardner TR, Levine WN, Bigliani LU. Biomechanical evaluation of subscapularis repair used during shoulder arthroplasty. J Shoulder Elbow Surg. 2007; 16(suppl 3):S59-S64. technique. J Shoulder Elbow Surg. 2009; 18(2):184-192. 2. Caplan JL, Whitfield B, Neviaser RJ. Subscapularis function after primary tendon to tendon repair in patients after replacement arthroplasty of the shoulder. J Shoulder Elbow Surg. 2009; 18(2):193-196. 8. Lapner PL, Sabri E, Rakhra K, Bell K, Athwal GS. Healing rates and subscapularis fatty infiltration after lesser tuberosity osteotomy versus subscapularis peel for exposure during shoulder arthroplasty. J Shoulder Elbow Surg. 2013; 22(3):396-402. 3. Fishman MP, Budge MD, Moravek JE Jr, et al. Biomechanical testing of small versus large lesser tuberosity osteotomies: effect on gap formation and ultimate failure load. J Shoulder Elbow Surg. 2014; 23(4):470476. 4. Giuseffi SA, Wongtriratanachai P, Omae H, et al. Biomechanical comparison of lesser tuberosity osteotomy versus subscapularis tenotomy in total shoulder arthroplasty. J Shoulder Elbow Surg. 2012; 21(8):10871095. 5. Jackson JD, Cil A, Smith J, Steinmann SP. Integrity and function of the subscapularis after total shoulder arthroplasty. J Shoulder Elbow Surg. 2010; 19(7):1085-1090. 6. Jandhyala S, Unnithan A, Hughes S, Hong T. Subscapularis tenotomy versus lesser tuberosity osteotomy during total shoulder replacement: a comparison of patient outcomes. J Shoulder Elbow Surg. 2011; 20(7):1102-1107. 7. Krishnan SG, Stewart DG, Reineck JR, Lin KC, Buzzell JE, Burkhead WZ. Subscapularis repair after shoulder arthroplasty: biomechanical and clinical validation of a novel SEPTEMBER/OCTOBER 2016 | Volume 39 • Number 5 9. Liem D, Kleeschulte K, Dedy N, Schulte TL, Steinbeck J, Marquardt B. Subscapularis function after transosseous repair in shoulder arthroplasty: transosseous subscapularis repair in shoulder arthroplasty. J Shoulder Elbow Surg. 2012; 21(10):1322-1327. 10. Van Thiel GS, Wang VM, Wang FC, et al. Biomechanical similarities among subscapularis repairs after shoulder arthroplasty. J Shoulder Elbow Surg. 2010; 19(5):657-663. 11.Scheibel MT, Habermeyer P. A modified Mason-Allen technique for rotator cuff repair using suture anchors. Arthroscopy. 2003; 19(3):330-333. 12. Miller BS, Joseph TA, Noonan TJ, Horan MP, Hawkins RJ. Rupture of the subscapularis tendon after shoulder arthroplasty: diagnosis, treatment, and outcome. J Shoulder Elbow Surg. 2005; 14(5):492-496. 13.Ponce BA, Ahluwalia RS, Mazzocca AD, Gobezie RG, Warner JJ, Millett PJ. Biomechanical and clinical evaluation of a novel lesser tuberosity repair technique in total shoulder arthroplasty. J Bone Joint Surg Am. 2005; 87(suppl 2):1-8. e943