In situ method to test skin extensibility for area excision

Abstracts-InternationalSocietyof BiomechanicsXIV Congress1993 IN SITU METHOD TO TEST SKIN EXTENSIBILITY FOR AREA EXCISION Kung-Chia Li, Pai-Chong Chiang, Jyh-Hong Yin, Rong-Hwang Fang, Jiunn-Jer Wu, WaiHee Lo. Dept of Orthopaedic Surgery & Plasty Surgery, Taipei-Veterans General Hospital, Taipei, Taiwan, 11217, R.O.C. Practically, the extent of skin excision is determined by individual experience and no scientific guide is available. We designed the in siru biomechanical method to measurethe skin load-elongation relationship to predict the maxima1safeareain once excision. The human subjectsin the study were 187 cases.Most of them were the patients and their families in the plasty surgery and traumatology divisions. The subjectswere assignedto 7 groups (decades)basedon their age. The female subjectswere about 22% to 39% in each group. The test site was selectedat the midpoint of right dorsal forearm sktn defined as the midpoint betweenlateral condyle and dorsal wrist. The dorsal forearm length, wrist width, and circumferenceof mid-forearm were measuredwith a flexible plastic ruler (k 0.1 mm), Single subcutaneoussuture was done with a 3-O Nylon at the midpoint of dorsal forearm under local anesthesia(2% Xylocain 0.2 ml). The suture line was connected to a weight-holder through a pulley. The traction weights of 0.3N, 0:8N, 1.3N, 2.3N, 3.2N, 4.2N, 5.2N, 6.2N and 7.2N were then applied sequentially within short period (5 set) in each step.Theaxis of traction was perpendicularto the long axis of the forearm. A ruler (zb0.1 mm) was attachedto measurethe elongationof the skin. The displacementwas recordedsequentially. In general, the forearm skin underwent the nonelastic deformation after 5.2N. The skin elongation showed significant difference between female and male, i.e. the female showed more skin elongation at the sameload. Neither male or female would the geometryof the forearm significantly affect the skin elongation. The group 4 of fifth decade showed significantly lesser elongation than the group 1, and also tend to be less than Group. Otherwisethe skin propertiessoundin pretty consistentcondition through 3rd decadeto 6 decade.

MODE OF FAILURE ANALYSIS LEADING TO NEW INSTRUMENTATION FOR THE ENHANCEMENT OF ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTIVE SURGERY Alan R.M.McLeodl,4, Kim C.Kong*, Michael A.S.Mowbrayz, Angus E.Strovers, William D.Cookel and Terrence K.O’Brien4 l-Department of Textiles, UMIST, PO Box 88, Manchester, M60 IQD, England 2-Mayday University Hospital, Thornton Heath, England 3Droitwich Knee Clinic, Droitwich, England 4-Surgicraft Ltd, Redditch, England Mode of failure analysis was performed on twenty-eight explanted ABC polyester and carbon fibre prosthetic anterior cruciate ligaments. Cleaned component strands were looped over a wire and tensile tested. Polyester strength was unchanged after implantation for 32 months. Carbon fibre cores with residual tissue ingrowth had increased in strength. Scanning electron microscopy found the damage to the prostheses to be localised to the exit of the tibia1 drill hole. Limited tensile breaks established that failure was not due to insufficient strength. Early ruptures were the result of focused crushing, flattening and fibrillation caused by impingement against the roof of to the intercondylar notch exacerbated by insufficient radiusing of the exit. Impingement is primarily the result of anterior placement. This can be avoided using a novel jig to place a guide wire posterior to an angled “rhino horn” probe which is held against the roof of the intercondylar notch. A study of five radiusing instruments resulted in a new cutter. This new instrumentation invariably locates a smoothly radiused exit posterior to the apex of the notch and should significantly reduce the incidence of impingement and mechanical damage in all forms of ACL reconstructive surgery.

JOINT POSITION SENSE IN SWOLLEN KNEES Peter J. McNair, Robert N. Marshall and Ken Maguire Faculty of Health Studies, Auckland Institute of Technology Auckland, New Zealand. This study investigated the effects of joint swelling on proprioception at the knee joint. Ten healthy subjects participated. One leg was passively moved through a range of motion from 90 degrees flexion to 10 degrees from full extension at a joint angular velocity of 60 deg/sec. Prior to the injection of fluid, subjects were blindfolded and required to track the passively moving joint as accurately as possible for a period of 1.25 minutes with the opposite limb. Ninety mls of a solution of saline and dextrose were then injected into the cavity of the knee joint. Subjects then repeated the tracking task. An electrogoniometer was used to monitor the motion of the limb which was tracking. Prior to the injection of fluid, the subjects moved their tracking limb ahead of the passively moved limb during extension and did not attain the same amount of extension as the passively moved limb (pO.O5).