Periprosthetic tissue metal content but not serum metal content predicts the type of tissue response in failed small-diameter metal-on-metal total hip arthroplasties.

BACKGROUND: Tissue responses to periprosthetic metal wear debris are complex and poorly understood. There are two predominant tissue responses: a nonspecific macrophage-mediated granulomatous response and lymphocyte-dominated response, which has immunological memory and is mediated by T cells. Delayed hypersensitivity-type responses may accelerate aseptic loosening of arthroplasty implants. We hypothesized that the metal content of periprosthetic tissue but not of serum would be predictive of the type of tissue response to metal wear debris. METHODS: We examined twenty-eight total hip arthroplasty implant retrievals from twenty-seven patients who had undergone revision arthroplasty at one institution. Indications for revision were pain and/or osteolysis; one patient had recurrent dislocations. Tissue samples were analyzed microscopically and the metal (Co, Cr, and Ni) content was determined. Explanted prosthetic components were examined for linear wear. Intraoperatively, periprosthetic metallosis was observed in twelve cases and formation of a bursa (pseudotumor) was observed in thirteen. The acetabular cup was loose in eleven cases, the femoral stem was loose in five, and both components were loose in five. RESULTS: The metal (Co, Cr, and Ni) content of the periprosthetic tissue ranged from 1.4 to 4604.0 µg/g. Histologically, macrophages containing metal particles as well as diffuse and perivascular lymphocytic infiltration were observed. Fibrin exudation was also visible. Tissues that displayed a predominantly lymphocytic response had a mean metal content of 222.2 ± 52.9 µg/g, whereas those that displayed a macrophage-dominated response had a metal content of 3.0 ± 0.9 µg/g; this difference was significant (p = 0.001). The mean serum metal content did not differ significantly between the two subgroups (60.7 ± 13.4 compared with 43.7 ± 3.8 µg/L, p = 0.105). CONCLUSIONS: An association between periprosthetic tissue metal content and hypersensitivity appears likely but needs to be validated with larger-scale retrieval studies. CLINICAL RELEVANCE: This study contributes to the understanding of tissue responses to metal wear debris after joint replacement and the factors that are predictive of a type-IV lymphocyte-dominated hypersensitivity reaction.

Does ligament balancing technique affect kinematics in rotating platform, PCL retaining knee arthroplasties? A prospective randomized study.

The goal of this prospective, randomized, blinded trial was to determine if ligament balancing techniques for rotating platform TKA affect postoperative knee kinematics. Sixteen patients with unilateral rotating platform TKA consented to participate in this institutional review board approved study. Eight patients were randomly selected to receive ligament balancing with an instrumented joint spreader device and eight patients received ligament balancing using fixed thickness spacer blocks. A single plane shape matching technique was used for kinematic analysis of static deep knee flexion and dynamic stair activities. There were no differences in knee kinematics between groups during static deep flexion activities. The spreader group demonstrated kinematics more similar to the normal knee during the ascending phase of the dynamic stair activity. Knee kinematics in static knee flexion were unaffected by ligament balancing technique, while knees balanced with the spreader demonstrated a medial pivot motion pattern during stair ascent. This medial pivot motion pattern may improve long-term results by more closely replicating normal knee kinematics.

Isometry of the posterior cruciate ligament. Effects of functional load and muscle force application.

The effects of functional load and muscle force application on isometry of the posterior cruciate ligament were determined. Eight fresh-frozen cadaver knees were mounted in a custom-designed rig. A full range of motion and muscle forces were applied through the quadriceps, hamstring, and gastrocnemius tendons during a simulated static squat maneuver. The low-load isometric posterior cruciate ligament point was located 5.63 mm proximal and 0.18 mm anterior to the anatomic center of the posterior cruciate ligament origin on the femur. The high-load state, with no gastrocnemius and hamstring muscle forces applied, shifted the isometric point 6.32 mm proximal and 6.72 mm anterior (P < 0.05). Loading the hamstring and gastrocnemius muscles also shifted the isometric point (P < 0.05). This study indicated that the most isometric region of the posterior cruciate ligament femoral attachment changed significantly when functional loads and muscle forces were applied to the knee. This finding may have implications for both surgical reconstruction and rehabilitation of the posterior cruciate ligament-injured knee.

[Importance of blade geometry for stability of fixation with short intramedullary nailing systems for the proximal end of the femur (gliding nail)]. / Die Bedeutung der Klingengeometrie für die Verankerungsstabilität bei kurzem Verriegelungsnagelsystem des proximalen Femurendes (Gleitnagel).

Three biomechanical examinations of the double-T blade of the gliding nail were performed. Under alternating load, also after 100,000 cycles and 2000 N load, no instability occurred after gliding nail osteosynthesis. The best relationship between the introduction forces of the blade (1.771-1.329 N) and the extraction forces (1.474-477 N) was seen after glass pearl treatment of the blade surface. Displacement of the plate in a sow bone femor head after 1000 cycles at 1500 N was 1.0-4.00 mm for a double-T blade, but 4.0-8.0 mm for a 10 mm screw like the gamma-nail screw.

Collagen shortening. An experimental approach with heat.

Decreasing joint laxity is a clinical goal of ligament reconstructions. This in vitro study examined the structural and histologic effects of heat shrinkage of human collagen. Two preliminary studies were performed to assess the effect of heat on fresh frozen human tendons obtained from a local tissue bank. As heat was applied to tissue in a saline solution, the percent shrinkage was plotted against temperature. A second study used a freebeam Nd:YAG laser to maximally shrink patellar tendons measuring percent shrinkage versus energy applied. Finally, the effects of 10% shrinkage of fresh frozen human patellar tendons were analyzed mechanically and histologically. Consistent tendon shrinkage curves were found with increasing temperatures in a saline solution. A sharp increase in shrinkage to approximately 70% of resting length was noted around 70 degrees C. Tendon shrinkage by laser induced heat was precise and dose related. Tensile testing of the tendons shortened 10% of their resting length showed a decrease in load to failure to approximately 1/3 compared with that of historical control specimens. Histologic sections showed a well demarcated site of diffuse denaturation and degeneration of collagenous elements. Normal collagen was present adjacent to these thermal changes. These experiments showed that collagen tissue can be shortened precisely by the application of heat. Future studies need to examine the in vivo biologic response of shortened collagen tissue with time, especially recollagenization, restoration of length, and the long term biomechanical effects.

Surgical management of intra- and postoperative fractures of the femur about the tip of the stem in total hip arthroplasty.

Six techniques for the surgical management of fractures of the femur about the tip of the stem of a total hip arthroplasty were evaluated. Seven embalmed human femurs were prepared to receive the correct-size femoral component of a total hip system. A transverse osteotomy was performed at the level of the tip of the stem. Stability and strength of each reconstruction were tested on each femur under semidynamic loading conditions. This study showed that cementless revision to a long-stem prosthesis does not provide adequate stability. The highest strength and stability were achieved by supplementing the long-stem conversion with allograft struts and cable cerclage. Good results were obtained by lateral compression plating with unicortical screws proximally. Failure was due to pull-out of the proximal screws.

Reconstruction with tenodesis in an adult flatfoot model. A biomechanical evaluation of four methods.

Six fresh-frozen adult cadaveric specimens were mounted in an Instron materials testing machine with use of a cemented intramedullary rod. Angular relationships between the first metatarsal and the talus were recorded with a sonic digitizer. A flatfoot deformity was created by dividing the talonavicular joint capsule (superiorly, medially, and inferiorly), the spring ligament, the anteromedial aspect of the subtalar joint capsule, and the plantar fascia. Angular displacement in the sagittal and transverse planes was recorded at no load and at 100, 350, and 700-newton plantar loads. Each specimen was subjected to four different reconstructions with tenodesis, and the angular relationship between the first metatarsal and the talus was measured at the four levels of load. A reconstruction with use of the peroneus longus tendon was performed by preserving its insertion into the first metatarsal, rerouting the tendon and passing it from medial to lateral through a calcaneal bone tunnel, and anchoring it to the lateral aspect of the calcaneus. A reconstruction with the tibialis tendon was performed by passing the medial third of the tendon from dorsal to plantar through the navicular and from medial to lateral through the calcaneal bone tunnel and securing it to the lateral aspect of the calcaneus. The reconstruction with the tibialis anterior tendon was repeated with the tendon graft routed along the medial aspect of the navicular, directly through the calcaneal bone tunnel. The fourth reconstruction was done with use of an Achilles tendon allograft.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamic support of the human longitudinal arch. A biomechanical evaluation.

This study was designed to evaluate the dynamic support provided to the human longitudinal arch by the leg muscles active in the stance phase of gait and by the plantar aponeurosis. Ten fresh adult cadaveric specimens were mounted in a materials testing machine. The tendons of the posterior tibialis, flexor digitorum longus, flexor hallucis longus, peroneus longus, peroneus brevis, and Achilles tendon were attached to force transducers. Plantar loads of 0, 350 and 700 N were applied, and the tendons were tensioned individually. The Achilles tendon was tensioned an amount equal to the plantar load; the posterior tibialis, flexor digitorum longus, flexor hallucis longus, peroneus longus, and peroneus brevis were tensioned a fractional amount (depending on the proportion of the cross-sectional area to the gastrocsoleus complex). The angular relationships between the first metatarsal, navicular, and talus were recorded using a 3-dimensional movement analysis system. An additional series of measurements was obtained by positioning the ankle plantarflexed 10 degrees under a plantar load of 350 N. Dorsiflexing the toes with the ankle in a neutral position and loading the foot to 350 N and 700 N permitted an evaluation of the effect of the plantar aponeurosis. The plantar aponeurosis, via dorsiflexion of the toes, contributed the most significant arch support in the sagittal plane with a 3.6 degrees increase between the first metatarsal and talus at 350 N and a 2.3 degrees increase at 700 N. The posterior tibialis tendon consistently provided arch support at plantar loads of 350 N and 700 N. The peroneus longus consistently abducted the forefoot in the transverse plane at 350-N and 700-N load levels. The study provides further insight into the dynamic supporting and deforming forces of the longitudinal arch.

Translation of the glenohumeral joint with simulated active elevation.

Translation of the glenohumeral joint was measured with a dynamic shoulder model during elevation of the arm in 8 cadaveric specimens. Controlled hydrodynamic actuator forces were applied to the deltoid muscle and the rotator cuff through wire cables. Using a constant force ratio, the glenohumeral joint was elevated to 90 degrees. The position of the arm in all spatial orientations was measured with an ultrasonic device. Reproducibility of glenohumeral joint motion was demonstrated on the basis of 5 cycles of glenohumeral joint elevation. The rotational center of the humeral head was used as the reference point for translation. Translation during elevation of the glenohumeral joint between 20 degrees and 90 degrees averaged 9.0 mm +/- 5.2 mm superiorly and 4.4 mm +/- 1.3 mm anteriorly. Physiologic variation of muscle activity, which is not yet fully understood, was not included in the model. In vivo, translation may be diminished by coordinated activity of the rotator cuff. The presence of significant glenohumeral joint translation underlines the importance of active, muscular guidance at the shoulder. Physiologic translation must be considered in the design of total shoulder arthroplasty, in shoulder instability, and in the impingement syndrome.

Corneal tensile strength in fully healed radial keratotomy wounds.

PURPOSE: To investigate the susceptibility to rupture of a human donor cornea with fully healed radial keratotomy (RK) incisions using biomechanical measurement methods and finite element analysis. METHODS: A human cornea 8 years after RK was cut into four strips and subjected to tensile testing until rupture occurred. The fellow cornea was pressurized on an artificial anterior chamber beyond the initiation of wound gape. The tensile strengths of nine strips from unincised corneas were measured as controls. To investigate the effect of epithelial plugs on the RK strip test results, a finite element model of a strip containing an epithelial plug was analyzed. RESULTS: Rupture occurred along the wound site with wide variability in the measured tensile strengths. There was no significant difference in tensile strength between the RK corneal strips (16.6 +/- 4.43 N/mm2) and the control strips (19.1 +/- 3.50 N/mm2). Four of the eight incisions of the fellow RK cornea gaped, but the cornea did not rupture up to a pressure of 2740 mm Hg. An epithelial plug of 10% of the corneal thickness was found in one of the incisions. The finite element results demonstrated higher stresses at the wound site that increased with the size of the epithelial plug. CONCLUSIONS: The presence of an epithelial plug in a fully healed radial keratotomy incision will create a stress concentration at the incision site that may predispose the cornea to rupture. The variability in the strength measurements indicates that the increase in rupture susceptibility due to RK may be hard to predict and may depend on factors such as the size of the plug and the strength of the wound collagen.

A comparison of various loading configurations of the proximal femur for the evaluation of reconstructive surgical procedures.

The study was designed to evaluate the effect of different loading configurations on stem and bone stresses in simulated total hip arthroplasty. The traditional experiment design of loading the model through the head of the prosthesis by the resultant joint force was compared with a more realistic model which included an abductor strap to simulate the abductor muscle force. In addition, an alternative experiment design was evaluated in which a loading arm was clamped directly on to the head of the prosthesis. The results show that loading the model by the resultant joint force not only changes the magnitude of the stresses but also the stress distribution compared to the abductor muscle model. The new experiment design closely approximates stresses seen in the abductor muscle model below the lesser trochanter. In the proximal region, the stresses are increased on the medial side and decreased on the lateral side. The advantages of the proposed loading model are: (a) easy and reproducible set-up and alignment is facilitated, (b) different positions of the femur (flexion, extension) can be simulated and (c) a more realistic stress distribution and magnitude is achieved.