Metallic versus biodegradable suture anchors for rotator cuff repair: a case control study

Case control study

Patients were included in the study if they underwent arthroscopic RCR and the following conditions were present at the time of surgery: RC tear, absence of shoulder instability, absence of shoulder’s fractures, MRI evidence of full-thickness RC tear, duration of symptoms of at least 3 months, inadequate response to non-operative management (including non-steroidal anti-inflammatory drugs, physiotherapy, rest, and one local corticosteroid injection), a repairable RC tear found at the time of surgery. Patients with pathology of the tendon of the long head of the biceps were also included in the study.

Exclusion criteria were: inflammatory joint disease, prior surgery on the affected shoulder, labral pathology, degenerative arthritis of the glenohumeral joint, symptomatic arthritis of the acromioclavicular joint, RC arthropathy, inability to complete questionnaires.

The mean follow up period were 4.05 + 2 year (range 1 to 10 years) from the surgery. Age; sex; arm dominance; history of trauma; location of RC tear; dimension of the RC tear; biceps tendon rupture or tendinopathy; type of treatment of biceps tendon; acromioplasty; number of anchors used; post-operative range of motion (ROM); post-operative modified University of California, Los Angeles (UCLA) [25] shoulder rating scale; post-operative Wolfgang criteria shoulder score; post-operative Oxford shoulder score (OSS) [26, 27]; post-operative strength of anterior elevation, external and internal rotation were evaluated.

A modified UCLA [25] shoulder rating scale was used to evaluate strength (5 points), shoulder pain (10 points), function (10 points), active forward flexion (5 points) and patient satisfaction (5 points). The maximum score obtainable is 35, and the results were classified as excellent (34–35 points), good (28–33), fair (21–27), or poor (0–20).

The Wolfgang criteria were used to assess post-operative shoulder pain (4 points), active abduction (4 points), strength (4 points) and patient satisfaction (1 point or minus 1 point). The maximum score obtainable is 17, and the results were classified as excellent (14–17 points), good (11–13 points), fair (8–10 points) or poor (0–7 points).

Postoperatively, all patients completed the Italian version of the (OSS) [26], a questionnaire that evaluates shoulder function, pain and strength in relationship with daily life activities. The minimum score is 12 points and the maximum score is 60 points. The higher is the score, the worse the condition of the shoulder.

Clinical and functional evaluations were performed by two blinded examiners. Patients were positioned supine with the shoulder at 90° of abduction in the scapular plane. Supine passive and active forward elevation (sagittal plane), internal and external rotation ROM (90° abduction) were evaluated with a standard universal goniometer [28].

A dynamometer (mod.CH 15 K20-KERN Balingen - Germany) was used to measure the strength of anterior elevation, internal and external rotation of the shoulder, and the results obtained were expressed in Newton (N). Both examiners performed three measurements for each ROM and strength measurement investigated. The average value for each variable was used for statistical purposes.

Patients were divided into two groups: metallic suture anchors (Group 1), or biodegradable suture anchors (Group 2). Demographic and surgical details of the patients enrolled in the study are shown in Table 1.

Arthroscopic RCRs were performed by two orthopaedic surgeons, expert in the use of both metallic and biodegradable implants.

Patients underwent brachial plexus block (associated, in 21 patients, with general anaesthesia). RCRs were performed with patients in a lateral decubitus position and the affected arm at approximately 45° of abduction and 20° of forward flexion. Distraction of the shoulder joint was accomplished with 4.5 to 6.5 kg of traction. A diagnostic arthroscopy was made. Bleeding was controlled using radiofrequency and adrenalin mixed to the irrigation fluid. A subacromial decompression was performed in the presence of a type III Acromion.

Footprint of the greater tuberosity was abraded. RCR was performed placing one row of suture anchors double loaded with N° 2 Fiberwire (Corkscrew, Arthrex, Naples, FL) (Group 1) or (Biocorkscrew, Arthrex, Naples, FL) (Group 2) just in the lateral aspect of the footprint. The number of suture anchors varied with the size of the tear. We used 2 or 3 suture anchors with a single row technique in patients with a tear larger than 3 cm and 1 suture anchor in patients with a tear < of 3 cm.

The two groups had the same post-operative management. Patients used a sling for the affected arm with an abduction pillow for 6 weeks. Movements allowed were: active elbow flexion; active elbow extension; passive external rotation. Terminal extension and overhead stretching were restricted until 6 weeks post-operatively and manual work and overhead activities were restricted until 12 months. Strengthening and rehabilitation of the rotator cuff, deltoid and scapular muscles were initiated at 10 or 12 weeks after surgery.

Statistical analyses were conducted considering the following outcome scores: total modified UCLA shoulder score, total Wolfgang criteria shoulder score and total OSS. We considered also active and passive ROM and strength of anterior elevation, internal rotation and external rotation. The independent variables analyzed were: age; sex; arm dominance; history of trauma; location and dimension of the rotator cuff tear; biceps tendon rupture or tendinopathy; type of treatment of biceps tendon; acromioplasty; number of anchors used. Comparison between the 2 groups for each independent variable was carried out with the Student t test for continuous variables and the × 2 test for categorical variables. The outcome variables considered (shoulder outcome scores, active and passive ROM, muscle strength) were compared using the Student t test. A one-way ANCOVA was performed to compare the effectiveness of the type of suture anchors on outcome scores, ROM and strength whilst controlling for the length of follow-up. The effect size was evaluated according Cohen’s guidelines: 0.2 - small effect, 0.5 - moderate effect, 0.8 - large effect. Significance was set at P < 0.05.

In the present study, we enrolled a series of 110 consecutive patients who underwent RC repair at our institution without an a priory power analysis. However, we undertook a post hoc power analysis using UCLA score. According to previous study, the UCLA shoulder score minimal clinically important difference is 2.96 points in the 35-point scale [29]. We estimated that our study had 90% of power with an alfa error probability of 0.05, an effect size of 0.65 and a minimum of 50 patients for each group.

The average of postoperative OSS was 23.7 + 11.4 points (range: 12–51).

The mean postoperative passive and active forward flexion, external and internal rotation ROM is reported in Table 3. Table 3 also lists the mean strength value in anterior elevation, external and in internal rotation ROM.

Four of the patients in this group were involved in recreational volleyball, and 3 in recreational soccer: all returned to their pre-injury levels of sports.

The average postoperative modified UCLA shoulder score was 27.7 + 6.5 points (range 6–35). \. According to the modified UCLA shoulder rating scale, 12 patients (20%) were excellent, 22 patients (37%) were good, 17 (29%) were fair, and the remaining 8 patients (14%) were poor.

The mean postoperative passive and active forward flexion, external and internal rotation ROM is reported in Table 4. Table 4 also lists the mean strength value in anterior elevation, external and in internal rotation ROM.

Two of the patients in this group were involved in recreational tennis, and both returned to their pre-injury levels of sports.

The comparison between the two groups did not show any statistically significant differences for any of the outcome variable considered.

Overall, the mean modified UCLA shoulder score was 26.9 + 7.1 points in group 1, and 27.7 + 6.5 in group 2 (P = 0.5); the mean Wolfgang criteria scores was 13.3 + 3.3 points in group 1, and 14 + 2.6 in group 2 (P = 0.3); the mean Oxford shoulder scores were 23.7 + 11.4 points in group 1, and 20.7 + 9.2 in group 2 (P = 0.1).

The mean passive anterior elevation was 169.4° + 23.6 in group 1, and 173.1° + 16.9 in group 2 (P = 0.3); the mean passive external rotation was 73.9° + 23° in group 1, and 74.4° + 20° in group 2 (P = 0.9); the mean passive internal rotation was 84.3° + 15.1° in group 1, and 83.5° + 15.9° in group 2 (P = 0.8). The mean active anterior elevation was 163.5° + 28.2° in group 1, and 163.6° + 26.9 in group 2 (P = 0.9); the mean active external rotation was 46° + 19.7° in group 1, and 44.6° + 16.3° in group 2 (P = 0.7).

The mean strength in anterior elevation was 48.02 + 23.52 N in group 1, and 43.12 + 17.64 N in group 2 (P = 0.2); the mean strength in external rotation was 48.02 + 22.54 N in group 1 and 46.06 + 17.64 N in group 2 (P = 0.6); the mean strength in internal rotation was 67.62 + 29.4 N in group 1, and 68.6 + 25.48 N in group 2 (P = 0.9).