We have developed a novel system of 4-dimensional motion analysis after total hip arthroplasty (THA) that can aid in preventing dislocation by assessing safe range of motion for patients in several daily activities.

This system uses skeletal structure data from CT and motion capture data from an infrared position sensor. A 3-D model reconstructed from CT data is combined with the motion capture data. Using this system, we analyzed hip motion when getting up from and sitting down in a chair or picking up an object while sitting in a chair in 17 patients (26 hips) who underwent THA. To assess the accuracy of this system’s measurements, open MRI was used to evaluate positions of skin markers against bones in 5 healthy volunteers in various postures.

No impingement between bones and/or implants was found in any subjects during any activities. However, mean angle at the point of maximum hip flexion was different for each patient. The open MRI results indicated that average error in hip angle of the present system was within 5 degrees for each static posture.

The functional position of the pelvis during daily activities must be taken into account when assessing the real risk of dislocation. The present system enables dynamic analysis involving not only alignment of components and bones of each patient, but also individual differences in characteristics of daily motions. Further investigation using this system can help determine safe ranges of motion for preventing hip dislocation, improving the accuracy of individualized guidance for patients regarding postoperative activities.

[Objectives] Hallux valgus, dorsal sublaxation or dislocation of metatarsophalangeal joints and clawing of the lateral toes are seen frequently in patients with rheumatoid arthritis (RA). Resection arthroplasty of the metatarsophalangeal joints (MTP joints) are widely used to correct these forefoot deformities and the clinical results are almost good. However lateral toes tend to displace dorsally and painful callosity tends to recur. We used the metatarsal shortening offset osteotomy for shortening and dorsal/medial displacement of the prominent metatarsal head. In this report, we introduce the surgical techniques of shortening offset osteotomy and postoperative changes of plantar pressure measured with F-scan system (Tekscan, Inc. ), and review the short term result during 1 to 4 year follow-up.

[Materials and Methods] This study involved 26 feet of 18 patients with RA which were performed with the metatarsal osteotomy for lateral toes and followed more than 1 year (average follow-up 29 months, range 14–46 months). The average age of the 17 women and 1 man was 61 years (range, 51–77 years). The mean duration from the onset of RA to operation on the forefoot was 17 years (range, 7–42 years). Skin incision was placed on the dorsum of the foot and the extensor digitorum brevis and longus were severed (or elongated). After reposition of MTP joint, transverse osteotomy of distal fifth of the lateral metatarsal bone was performed with resection of few millimeters length metaphysial bone. Cortical bone of the distal end of the proximal stump was chiseled into a small rod between two ditches with rongeur and then the rod was put into medullary canal mortise of distal stump. This procedure make offset shift of metatarsal head medially or dorsally. Swanson implant arthroplasty, distal osteotomy was performed on the great toe. Postoperative clinical and radiological results were evaluated with AOFAS rating system. We measured dynamic plantar pressure before and one year after operation in one representative case.

[Results] At the time of follow-up, the mean AOFAS score was 80 points (59–95) and the mean pain score was 36 points. The recurrence of painful callosity was one case. Nevertheless, the range of motion of the MTP joint remained low: 30 degrees and less in 16 feet (62%) including 3 bony ankylosis of MTP joints. There was no nonunion case. [Discussion]

Resection arthroplasty has been accepted as the treatment of choice for forefoot deformities in RA patients. Recent advance of drug therapy against RA encouraged us to preserve the joint in correction of forefoot deformities. Our technique aimed at preservation of the function of the MTP joints and is suitable for mild deformities in which only one or two rays are involved. Furthermore it is easy to correct the deformity of spray foot and reduce the plantar prominence of metatarsal head. This study revealed the good clinical result in short term follow-up. Although the long term result must to be waited, this method is one of recommendable options for RA patients with forefoot deformities.