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Hypothesis: In the surgical treatment of thumb carpometacarpal (CMC) joint arthritis, patients with less than 30 degrees of metacarpophalangeal (MCP) joint hyperextension have improved functional outcomes compared to those with greater than 30 degrees of deformity.

Methods: A retrospective review was conducted analyzing the outcomes of patients treated for CMC arthritis and MCP hyperextension deformity from 1990-2009.  Patients were included if they underwent simultaneous treatment of CMC joint arthritis and a procedure to address the MCP hyperextension deformity. Standardized pre and postoperative assessments included pinch & grip strength, MCP range of motion (ROM), degree of MCP hyperextension (less than or greater than 30 degrees), thumb interphalangeal (IP) ROM and thumb radial and palmar abduction. Radiographs were examined to determine the degree of 1^st metacarpal subsidence postoperatively. Statistical analyses used included parametric t tests.

Results: Thirty five patients met the inclusion criteria and were followed for an average of 25.2 months (Range: 1.3 to 105 months).  Thirty one patients underwent trapeziectomy and suspension arthroplasty and 4 had a CMC hemi-arthroplasty. There were 19 patients who had preoperative MCP joint extension less than 30 degrees and 16 greater than 30 degrees. Fifteen patients underwent MCP joint capsulodesis, 17 had MCP joint fusions and 3 were temporarily pinned.  The average post operative MCP hyperextension was 2.44 and 4.34 degrees in each of the MCP joint hyperextension groups (Chart 1). There were no statistically significant differences with respect to improvement in range of motion, pinch and grip strength, and subsidence of the 1^st metacarpal between the 2 groups.  Similarly, there were no differences with regards to improvement in functional outcomes between the patients treated with MCP joint capsulodesis versus fusion. The capsulodesis patients were devoid of any major complications compared to those who had undergone MCP joint fusion (1 pulmonary embolism, 2 patients with extensor tendon tethering by hardware, 1 with symptomatic hardware requiring removal and 1 non-union). 

Summary:

- The degree of pre-operative MCP hyperextension deformity did not affect the improvement in functional outcomes in our series.

- Method of treatment of MCP hyperextension deformity did not affect the improvement in functional outcome, but patients undergoing MCP fusion tended to have worse pre-operative hyperextension deformities and sustained a higher number of major complications.