A biomechanical study of the effects of simulated ulnar deviation on silicone finger joint implant failure

Silicone finger arthroplasties are used widely, especially for metacarpophalangeal joint replacement in patients with inflammatory arthritis. Implant failure is well recognized. The rates of failure in vivo differ substantially from experience in vivo. One cause of failure is felt to be post-operative ulnar deviation. The aim of our study was to test the effect of ulnar deviation testing on silicone finger implants. We tested 12 implants in three groups of four implants. The implants were submerged in a bath of Ringer’s solution at 370 °C throughout the experiment and tested in a rig held in 0°, 10° and 20° deviation. The rig was cycled at 1.5 Hz from 0°–90°. The implants were inspected every 500,000 cycles until a total of 4 million cycles. There was consistently increased wear and supination plastic deformity in going from 0°–20° deviation. This study confirms the adverse effects of ulnar deviation on silicone finger implant wear. It is likely that this combines with lateral pinch forces and sharp bone edges to cause catastrophic silicone implant failure. Level of evidence: III </jats:p

Beware of the ulno-palmar distal radial fragment

Five patients sustained isolated fractures of the ulnopalmar rim of the distal radius. In three cases the fragment was small and was classed as an avulsion fracture of the short radiolunate ligament. Palmar wrist subluxation occurred in all cases, four during treatment in a cast or splint. The ulnopalmar rim of the distal radius contributes to the stability of the radiocarpal joint and fractures in this region merit particular attention

The reliability of clinical assessment of distal radioulnar joint instability

Accurate assessment of distal radioulnar joint (DRUJ) stability is increasingly recognized as an important part of clinical examination of the wrist. The ability of 30 specialist UK hand surgeons to clinically determine the stability of four volunteers' wrists was assessed. Volunteers' wrist stability had previously been confirmed with a validated measurement rig. Use of the wrist ballottement test as the primary examination technique yielded a positive predictive value of 81%, a negative predictive value of 55%, a specificity of 94% and a sensitivity of only 24%, for the detection of DRUJ instability. No correlation between background speciality (orthopaedic versus plastic surgery), nor years of clinical experience was found. Clinical assessment of DRUJ instability among experienced clinicians appears unreliable and instability is typically under recognized. Previous research to date using this clinical assessment method as a parameter of success is therefore brought into question.Level of evidence: IV.RD&E staff can access the full-text of this article by clicking on the 'Additional Link' above and logging in with NHS OpenAthens if prompted.Published version, accepted versio