Impact of radiocapitellar interposition arthroplasty on ulnohumeral joint biomechanics.

BACKGROUND: Radial head excision (RHE) has been shown to increase contact pressures within the ulnohumeral joint. Radiocapitellar interposition arthroplasty (RCIA) with the use of a soft tissue graft is an alternative for the treatment of isolated radiocapitellar arthritis or with failure of radial head replacement. We investigated contact pressures and contact area within the ulnohumeral joint after RHE compared to RCIA with dermal autograft. METHODS: Six fresh-frozen cadaver elbows were tested on a custom dynamic elbow frame. A pressure sensor was inserted into the intact elbow joint, and mean contact pressure, peak contact pressure, contact area, and force within the ulnohumeral joint were recorded at 0°, 30°, 60°, 90°, and 120° of flexion as a valgus load was applied to the elbow. The radial head was then excised and specimens were retested. Finally, a dermal graft matched to the size of the resected radial head was inserted in the radiocapitellar space and the specimens were tested a third time. RESULTS: At 90° of flexion, contact pressure within the ulnohumeral joint was significantly lower with RCIA compared with RHE (110.8 kPa vs 216.8 kPa; P = .013). The mean peak contact pressure was also significantly lower with RCIA compared with RHE at 90° (279.4 vs 626.7 kPa; P = .025). No statistically significant differences were seen in mean contact area or force between the 3 testing conditions at any flexion position. CONCLUSION: RCIA with a dermal graft reduced contact pressures within the ulnohumeral joint compared to RHE at 90° of flexion without a significant change in contact area or contact force.

Effect of glenosphere lateralization with and without coracoacromial ligament transection on acromial and scapular spine strain in reverse shoulder arthroplasty.

Background: Small changes in deltoid tension and moment arm due to glenosphere lateralization may be associated with an increase in acromion or scapular spine strain in reverse shoulder arthroplasty (RSA), which can lead to stress fracture. The coracoacromial ligament (CAL) may be protective and lower the strain seen on the acromion or scapular spine. This biomechanical study investigated the impact of glenosphere lateralization and CAL integrity on acromion and scapular spine strain after RSA. Methods: Ten cadaveric specimens were tested on a custom dynamic shoulder frame. Acromial and scapular spine strain were measured at 0°, 30°, and 60° of abduction using strain rosettes fixed to the acromion (Levy Type 2) and the scapular spine (Levy Type 3). Specimens were first tested with a standard commercially available RSA implant with zero lateralization and then subsequently with the +3 and +6 lateralizing glenospheres for that implant. The CAL was then cut in each specimen and testing was repeated with the 0, +3, and +6 glenospheres. Maximal strain was recorded at both the acromion and scapular spine and analysis of variance compared strain across various abduction angles and glenospheres with and without CAL transection. Results: In the intact CAL group, maximal strain decreased significantly at the acromion with abduction from 0° to 30° and 0° to 60°, however, at the scapular spine abduction did not significantly impact strain. Maximal strain decreased significantly with increasing abduction from 0 to 30 and 0 to 60 at both the acromion and scapular spine in the cut CAL group. Average strain at the acromion was significantly higher in the cut group (844.7 µÎµ) versus the intact group (580.3 µÎµ), a difference of 31.3% (P = .0493). Average strain at the scapular spine, did not differ in the cut group (725 µÎµ) compared with the intact group (787 µÎµ) (P = .3666). There were no statistically significant differences in acromial or scapular spine strain between various levels of glenosphere lateralization in either the cut or intact state. Conclusion: In this biomechanical study, arm abduction decreased acromial and scapular spine strain following RSA. Cutting the CAL significantly increased strain at the acromion, and did not significantly alter strain at the scapular spine for all angles of abduction, differing from prior literature. Glenosphere lateralization did not have a significant effect on strain at the levels studied regardless of CAL status. Continued study of the complexion relationship between surgical and implant factors on strain following RSA is needed.

The Central-Splitting Approach for Achilles Insertional Tendinopathy and Haglund Deformity.

Insertional Achilles tendinopathy causes posterior heel pain at the insertion of the Achilles tendon, often in combination with a calcaneal exostosis, or Haglund deformity. Insertional Achilles tendinopathy often presents with a posterior osseous prominence and leads to calcification of the Achilles tendon1. Nonoperative treatment of these conditions includes activity modification, nonsteroidal anti-inflammatory agents, heel lifts, shoe modification, physical therapy focused on eccentric strengthening exercises, iontophoresis, and shock wave therapy. Nonoperative treatment will fail in approximately 50% of these cases, and such patients become candidates for surgical intervention2,3. Multiple surgical approaches have been described, including the medial J-shaped, lateral, Cincinnati transverse, double incision, and central-splitting approaches4. Currently, there is no consensus regarding the ideal approach. Recent literature has suggested that the central-splitting approach allows for adequate exposure of both the most commonly diseased area of the tendon and the calcaneal exostosis, with excellent postoperative pain and functional results5-13. DESCRIPTION: Place the patient in the prone position with the feet at the edge of the operating table. Make a full-thickness, 5 to 7-cm longitudinal incision centered over the Achilles tendon and the posterior aspect of the calcaneus. Make a central incision through the Achilles tendon. Sharply mobilize the medial and lateral slips and excise the diseased portion of the Achilles tendon. Expose the calcaneal exostosis and perform the calcaneal exostectomy with a microsagittal saw. Repair the remaining healthy-appearing Achilles tendon to the calcaneus with 2 suture anchors. An additional suture anchor or, alternatively, the double-row technique for the Achilles tendon repair may be used. Repair the central split in the Achilles tendon with absorbable suture. Close the soft tissue and skin in layers. ALTERNATIVES: Alternative approaches include the medial, lateral, or Cincinnati transverse incisions. The central-splitting approach is favored because of the excellent exposure of both the diseased tendon and the calcaneal exostosis. Additional augmentations to this procedure include a flexor hallucis longus transfer and a gastrocnemius recession. RATIONALE: This technique provides adequate exposure to the diseased Achilles tendon, calcific deposits, and calcaneal exostosis. Recent studies have demonstrated it to be a safe and effective technique with high patient-satisfaction scores5-13.