Linscheid, Ronald L.

Total joint arthroplasty (TJA) is implemented primarily for the relief of pain, and secondarily for achieving better function by increasing the joint’s strength and motion. In order to keep health costs low, it is desirable that the TJA achieves and maintains a long-term and secure fixation of the implanted components. Unfortunately, clinical follow-up shows that the prosthetic finger implant components have long-term complications including bone resorption, wear, loosening, and failure of the implant components. Although the mechanism of complications is not fully understood, it is well known that the wear and failure of prostheses are highly related to the mechanical forces or stresses of implant components. It is therefore desirable that reliable 3-D computational finite element analysis (FEA) models can be developed and used for the stress analysis of implants. In this study, the finger proximal interphalangeal (PIP) prosthetic components were analyzed using a nonlinear finite element method. Implant components under different joint flexion angles as well as different forces were studied. The stress distribution on the contact surface of the implant component was obtained. The developed FEA models can be used to examine the contact situations (contact stress, contact region, and stress distribution), which are critical to the wear and potential failure of the implant components. Based on FEA results, the design of the current finger PIP implants can be improved for optimum performance and a long-term fixation.

Twenty patients with Kienböck’s disease who had undergone a joint levelling procedure, were reviewed at a mean of 11 years following surgery. Clinical and radiological evaluation revealed good long-term results with all patients complaining of less pain than before surgery and with statistically significant increases in range of motion and grip strength. Radiologically a significant number of patients were found still to have lunate fractures and fragmentation. In addition, 13 patients have developed new bone formation in the lunate fossa, and 12 show osteoarthritic changes, particularly at the radioscaphoid interface. Radial shortening was felt to be superior to ulnar lengthening in that there were fewer problems with bone union.

A retrospective study of 45 patients with symptoms of wrist pain and weakness with clinical evidence of instability is presented. These patients had normal intrinsic interosseous ligaments demonstrated arthrographically or surgically. They were followed for a minimum of 18 months and an average of 5.8 years. All patients demonstrated instability of the proximal carpal row which is referred to as carpal instability non-dissociative (CIND). Seven patients were treated non-operatively and 38 were treated operatively. Surgical management consisted of soft tissue reconstruction directed at the area of instability in 34 cases, joint levelling osteotomy in six, three of whom also had soft tissue reconstructions, and mid-carpal fusion in one. The overall good and excellent results were a disappointing 56% and there was no significant difference between the non-surgical and surgical groups. The best results were found in the ulna-minus CIND patients who underwent a joint levelling osteotomy, with 83% good and excellent results. CIND is associatedwith extrinsic ligamentous laxity; however, significant difficulty exists in locating the precise areas of maximum pathology. This accounts for the unpredictable results of treatment. As our understanding of the pathomechanics of CIND improves, the treatment will become more specific and the results should improve.

Pisotriquetral arthrosis in young patients is considered rare and the diagnosis may be difficult to distinguish from other ulno-carpal problems. 12 patients under 40 years of age (15 cases) who underwent pisiformectomy were reviewed at a mean of 41 months. Patients with a good history of trauma and a positive response to intra-articular local anaesthetic injection did well. Others with an indefinite history and bilateral symptoms did not do so well. Trispiral tomography is the radiological investigation of choice.

Muscle physiological cross-sectional area, as defined and measured by dividing the volume of the muscle by its fibre length, is proportional to the maximum strength of the muscle. It is one of the important parameters when considering muscle mechanics in sports science and, clinically in tendon transfer procedures. This study reports that tendon cross-sectional area correlated well with the physiological cross-sectional area of associated muscles.

Abstract Carpal instability can be defined as the lack of ligamentous and skeletal support adequate to maintain a wrist stable to external forces of pinch and grasp. This instability may be static or dynamic. It has been classified as (a) carpal instability, dissociated (CID), a situation in which one or more of the ligaments are torn, and (b) carpal instability, nondissociative (CIND), a situation in which the ligaments are intact but stretched. Carpal instability can also be the result of carpal bone malalignment from various causes. Arthroscopy can be particularly useful in assessing carpal instability, however arthrography with contrast medium, fluoroscopy, and stress loading should precede this arthroscopic assessment. Arthroscopy allows visualization of the volar radiocarpal and ulnocarpal ligaments of the wrist, and the arthroscopic examination can be combined with manual manipulation of the carpal bones to detect laxity of those ligaments, to examine stability of the scapholunate and lunotriquetral interosseous ligaments, and to show instability of the distal radioulnar joint.