A new concept for tuberosity repair in hemiarthroplasty for fracture: use of a clamp and underlying ledge to form a trapdoor.

BACKGROUND: Sutures are the most common method for tuberosity repair in hemiarthroplasty for fracture. Despite numerous suggested patterns, tuberosity repair remains a weak point leading to poor functional results. This study mechanically tested a new mechanism that avoids difficulties sutures may engender. The hallmark of the prosthesis is a "trapdoor" effect. Low-profile metallic clamps with undersurface stoppers are screwed across the tuberosity-tendon junction to an underlying ledge, creating a fixed metallic space. With cuff contraction, the tuberosities are too large to pull through this space. MATERIALS AND METHODS: Tests were carried out in line with the U.K. Human Tissue Authority regulations. Four-part fractures in 8 cadavers repaired with this method were subjected to simultaneous cyclic tension of 350N and passive glenohumeral motion for 8000 cycles. Both before and after machine stress, repairs were assessed by clasping each tuberosity with a forceps and attempting to displace it in a variety of directions. No movement was present before stressing. Any post-stress movement was considered a failure and recorded in millimeters. RESULTS: Six specimens after machine stress showed 0-mm movement (95% confidence interval, 34.9%-96.8%). Isolated movements of a single tuberosity occurred in 2 specimens. CONCLUSION AND DISCUSSION: The trapdoor completely withstood challenging elements of cyclic load and passive motion in 75% of cases. The device may represent an alternative to sutures.

Is failure of tuberosity suture repair in hemi-arthroplasty for fracture mechanical?

BACKGROUND: Tuberosity suture repair in hemiarthroplasty for fracture carries risk of malunion giving poor results. Is failure mechanical or biochemical? We investigated the mechanical aspect with repetitive loading in cadaveric repairs. MATERIALS AND METHODS: Tests were carried out in line with U.K. Human Tissue Authority regulations. A 4-part fracture was created in 8 cadaver shoulders by osteotomizing the tuberosities. A standard hemiarthroplasty implant was cemented in at correct height and retroversion, and standardized repairs applied. Initial firmness of repair was confirmed by attempting to manually displace the tuberosities with a forceps in multiple planes. All pre-stress tests showed 0 mm movement. Repairs were then subjected to cyclical tension on the cuff musculature and simultaneous gleno-humeral motion for 8000 cycles. The tuberosities were reprobed with a forceps to record any movement. RESULTS: Defining repair failure as the ability to manually displace a tuberosity more than 3 mm, every specimen failed: 100% failure (exact 95% confidence interval 65.2-100% due to sample size). Movements of at least 1 cm were commonly observed. The sutures were loose but had never snapped. Sutures were noted to dig into the tendon and cut partially through bone. Collapse of cancellous bony volume led to looseness and migration of the sutures. CONCLUSION: Suture repair of tuberosities has mechanical weaknesses; failure may be a mechanical phenomenon.