ABSTRACTS 373

with a clinical diagnosis of instability. Patients were evaluated via (1) physical exam-normal vs abnormal shoulder, (2) CINE MRI-normal vs abnormal shoul- der, and (3) arthroscopic or open surgery which served as confirmation of the initial diagnoses.

Method: A shoulder CINE device which consisted of a self-indexing patient directed extremity stabiliza- tion system was used to obtain images. 20 patients rotated their arms from maximum internal to external rotation in fixed 10 ° increments. 8 to 16 axial images were taken utilizing a Midfield 0.6 Tesla magnet. The images were processed into hard copy as well as video- tape loop and then evaluated by a single, independent radiologist who was blinded to clinical and surgical findings.

Results: Consistent variations of the capsulolabral complex were identified on the painful and painfree shoulder. CINE MRI consistently diagnosed labral pa- thology (SLAP lesions were not evaluated in this study). Capsular stripping and capsular detachment as well as excess glenohumeral translation were also ob- served with CINE MRI.

Discussion and Conclusion: CINE MRI findings for anterior instability were anterior humeral head notching, stripping of the capsule off the glenoid neck and migration of the capsulolabral complex antero- medially in maximum internal rotation. For posterior instability, posterior humeral head translation and cap- sulolabral migration posteriorly were identified in maximum external rotation. These findings were con- firmed during surgery.

Relationship Between Ultimate Load, Tendon Slip, and Installation Torque for Washer Fixation of Tendon to Bone. Todd W. Wright, Ronald J. Ender, and Ben K. Graf Madison, Wisconsin, U.S.A.

Different bicortical screws and washers for tibial fixation of hamstring ACL reconstructions were com- pared. Tendon slip past the fixation site was measured and used as a definition of failure. Screw insertion torque was recorded and correlated with the fixation strength for the constructs tested. The devices com- pared were 4.5-mm bicortical screws with 14-mm Con- cept spiked washers, 20-ram Concept spiked washers, 13.5 x 6 mm Synthes plastic spiked washers, and 13.5 x 4 mm Synthes plastic spiked washer. Five porcine tibias and extensor tendon sets were harvested for each test subset. Tendons were grouped using an 8-mm di- ameter sizer and the tibias prepared with a 9-mm reamer that produced a 4-cm-long tunnel. The fixation device and tendon construct were fixed to the tibial

metaphysis using a prescribed torque. Load was ap- plied to the tendons parallel to the tibial tunnel on a universal testing machine. Each construct was loaded in tension at a rate of 1 mm/second. Load was recorded and tendon slip at the fixation device was measured using an extensometer.

All constructs failed at the fixation site. All con- structs allowed 0.1-mm tendon slip at the fixation site at loads 25% to 50% of the ultimate fixation strength. Slip at the fixation site at maximum load averaged 6.6 mm for the Concept and 4.6 mm for the Synthes. At 15-inlb torque the Synthes 13.5 x 4 mm produced a higher maximum load (470.4 N) when compared to the Concept 20-ram (364 N, P = .04) and 14-mm (334 N, P = .01) washers. Load at 0.1-mm slip was also higher for Synthes (211 N) when compared to Concept 20-mm (91 N, P -- .003) and 14-mm (107 N, P = .008) washers. The 13.5 x 6 mm Synthes washer consistently failed by fracturing at a low installation torque (mean, 8.68 inlh) when installed with the rec- ommended 4.5-ram screw. Load at 0.1-mm slip and maximum load had a significant correlation to installa- tion torque for the Synthes and Concept washers (P < .05).

This study demonstrates that for the devices tested, tendon slip occurs well before maximum load is at- tained. Since slip is not recoverable, and might be cummulative under repetitive loading, the maximum load prior to slip may be a more clinically useful com- parative measure of fixation strength than maximum load. Furthermore, strength of fixation was found to be related to initial installation torque and washer de- sign. The 13.5 X 6 mm Synthes washer consistently cracked in use and cannot be recommended.

Patient Selection for Arthroscopic Shoulder Stabili- zation. Michael J. Pagnani, Allen F. Anderson, Russell F. Warren, and David W. Altchek. Nashville, Tennes- see, and New York, New York, U.S.A.

Introduction: The risk of recurrent instability after arthroscopic shoulder stabilization is currently higher than that after an open procedure. Several reports have revealed recurrence rates of 15-20% after arthroscopic stabilization. This study attempts to assess factors asso- ciated with failure after arthroscopic stabilization and to narrow surgical indications in order to improve re- sults.

Methods: In the first part of the study, a retrospec- tive review of 102 patients who had undergone an arthroscopic stabilization procedure for anterior insta- bility, we specifically analyzed 4 "risk factors" to

Arthroscopy, Vol 12, No 3, 1996