William L. Buford

A comparison of double-plate fixation methods for complex distal humerus fractures

A modified method of fracture fixation of complex distal humeral fractures with medial and lateral plates and bolts was biomechanically tested and compared with previously described fixation techniques. Compressive stiffness coefficients were determined for three classes of fixation before and after fatigue cycling. This procedure was followed with compressive loading to failure. The results show that in the most unstable fracture type tested this new fixation method provides increased strength and stability. Early clinical follow-up examinations of patients treated with this technique show that this method is a reasonable fixation alternative for the complex distal humerus intercondylar fracture.

Muscle balance at the knee-moment arms for the normal knee and the ACL-minus knee

Forces, moments and stresses at the knee are dependent upon external and internal loading factors including muscle forces, segmental position and velocity, load carried, and the moment arms (mechanical advantage) of the muscle-tendon units. Requisite to prediction of forces and moments is a detailed understanding of effective moment arms throughout the knee range-of-motion (ROM). Existing muscle models for the knee are based upon limited static studies of only a few preserved specimens. The objectives of this report are to develop a comprehensive description of muscle-tendon moment arms for the normal knee and the anterior cruciate ligament (ACL)-minus knee during flexion-extension motion. Recent research results describe two nonorthogonal, nonintersecting axes of motion for the knee--one describing flexion-extension (FE) and the other longitudinal rotation (LR, equivalent to internal-external rotation). The effective flexion-extension moment arms of the muscles crossing the knee were developed with respect to the FE axis in 15 fresh, hemi-pelvis cadaver specimens. The normal moment arms for each of 13 muscles plus the patellar tendon exhibited variable, yet repeatable and recognizable patterns throughout the ROM. For most muscles there was no significant difference between the normal and ACL-minus moment arms. The results provide a basis for more accurate predictions of joint reaction forces and moments as well as useful knowledge for practitioners and therapists to assist in the assessment of muscle balance at the knee following injury, repair, and throughout rehabilitation.

A virtual five-link model of the thumb

Most researchers have modelled the thumb as three rigid links with connections of two universal joints (carpometacarpal joint and metacarpo-phalangeal joint), and a hinge joint (interphalangeal joint). Although this produces the required number of degrees of freedom, the resulting motion is not anatomically accurate. In this work, the thumb is modelled as a five-link manipulator with the virtual links connected by hinge joints-one for each degree of freedom of the thumb. The axes of the hinges are not orthogonal to one another, in the long axis of the bones or to the anatomic planes. Four static positions of hand function were analysed-key pinch, screwdriver hold, tip pinch, and wide grasp. The virtual five-link model of the thumb predicted similar muscle recruitment patterns to published EMG data. The force at the distal surface of the trapezium is between 6 and 24 times the applied load depending on the posture.

The axes of rotation of the thumb interphalangeal and metacarpophalangeal joints

The axes of rotation of the thumb interphalangeal and metacarpophalangeal joints were located using a mechanical method. The interphalangeal joint axis is parallel to the flexion crease of the joint and is not perpendicular to the phalanx. This offset of the axis with respect to the phalanx explains the ulnar deviation and pronation that occurs with flexion of the interphalangeal joint. The metacarpophalangeal joint has 2 fixed axes: a fixed flexion-extension axis just distal and volar to the epicondyles, and an abduction-adduction axis related to the proximal phalanx passing between the sesamoids. Neither axis is perpendicular to the phalanges. All physiologic motion for these joints occurs about the axes. These are the mechanical axes of the joints through which the muscles and external forces act. Knowledge of their location should help in constructing prosthetic joints and in planning reconstructive surgery such as tendon transfers.

Anatomy and pathomechanics of ring and small finger carpometacarpal joint injuries.

PURPOSE The purpose of this study was to detail the pathomechanics and pathoanatomy of fracture dislocations of the ring finger and small finger carpometacarpal (CMC) joint by duplicating the pathomechanics of the fist blow. METHODS A custom-made jig was used to position 20 fresh-frozen cadaver upper extremities in forearm neutral rotation, 90 degrees of elbow flexion, 20 degrees of wrist extension, and 20 degrees and 30 degrees of flexion at the ring and small finger CMC joint, respectively. First 7.7 kg of weight were dropped from a height of 0.76 m to 1.1 m to axially load the ring and small metacarpal (MC) heads through a custom-made apparatus. Fluoroscopic examination before and after loading, and detailed dissection after loading, were used to identify any osseous and/or ligamentous injuries. RESULTS The most common fractures were a dorsal capitate fracture and a middle MC dorsal base fracture. The most common combinations of fractures were the dorsal capitate and dorsal hamate fractures. Multiple fractures often were identified in a number of locations including dorsally: the capitate, hamate, and index through small metacarpal bases, and volarly: the hook of the hamate and the middle through the small MC bases. CONCLUSIONS The patterns of injuries encountered at the ring and small CMC joints can be explained by the direction and force of the applied load, position of the CMC joint at the time of loading, and the constraints imposed by specific CMC ligaments. A detailed analysis of the fracture patterns and associated ligament anatomy suggests that the typical ring and small carpometacarpal fracture dislocations are a more complex combination of fractures than identified by plain radiographs alone. The complexity of these injuries is greater than previously recognized and is most likely the result of a combination of axial load and shear stresses resulting in carpal fractures and ligament avulsions as well as fracture dislocations. This study suggests that computed tomography may be the preferred diagnostic imaging method for complete assessment of these injuries.

Carpal bone anatomy measured by computer analysis of three-dimensional reconstructions of computed tomography images

Using quantitative analysis of three-dimensional reconstructions of computed tomography scan data, a normative database of carpal bone morphology was built. Thirty-five wrists were imaged in a computed tomography scanner. Each slice was processed to determine the bone edges and assembled as a three-dimensional model by stacking. Quantitative measurements of volume, surface area, maximum length, and intercarpal distances were then assessed. A reliable three-dimensional carpal height ratio was calculated by dividing the carpal height (minimum distance between the fourth metacarpal and the radius) by the capitate maximum length. For volume, maximum length, and surface area, the order for the eight carpal bones with respect to size (in descending order) were: capitate, hamate, scaphoid, trapezium, lunate, trapezoid, triquetrum, and pisiform. Male wrists were significantly larger than female wrists. There were no significant differences in the relative dimensions between left and right wrists, or between left and right wrists of matched pairs. This technology offers automated analysis of three-dimensional geometric carpal information and the opportunity to obtain a body of information about normal and abnormal morphology as well as spatial relationships between carpal bones.

Three Femoral Fixation Devices for Anterior Cruciate Ligament Reconstruction: Comparison of Fixation on the Lateral Cortex Versus the Anterior Cortex

PURPOSE To evaluate the biomechanical properties of 3 anterior cruciate ligament (ACL) reconstruction femoral fixation devices in a porcine model with implantation on both the lateral femoral cortex and the anterior femoral cortex. METHODS ACL reconstructions with an 8-mm porcine tendon graft were performed on 48 porcine femurs with the EndoButton CL (Smith & Nephew, Andover, MA), ToggleLoc with ZipLoop technology (Biomet Sports Medicine, Warsaw, IN), or EZLoc (Biomet Sports Medicine). In 8 specimens for each implant, the femoral tunnel was drilled from the 10:30 surgical position out the lateral cortex. In another 8 specimens for each implant, the tunnel was drilled from the 10:30 position to a standardized anterior femoral surface. Cyclic testing was performed on an MTS testing machine (MTS, Eden Prairie, MN) from 50 N to 450 N for 2,000 cycles, followed by load-to-failure testing in specimens that survived. The cortical thickness and location of the implant exit were recorded. RESULTS In the lateral femur group, 0 of the EZLoc devices, 2 of the ToggleLoc devices, and 3 of the EndoButtons completed cyclic testing. In the anterior femur group, 1 of the EZLoc devices, 5 of the ToggleLoc devices, and 5 of the EndoButtons completed cyclic testing (P = .012). In the anterior femur group, the ToggleLoc exhibited higher 2,000-cycle elongation (5.46 +/- 1 mm) than the EndoButton (3.55 +/- 0.6 mm) (P = .005). The EndoButton showed a higher first failure load (1,190.9 +/- 150.0 N) than the ToggleLoc (912.6 +/- 82.4 N) (P = .007). The anterior cortex (1.4 mm) was thinner than the lateral cortex (1.7 mm) (P = .0002). CONCLUSIONS The EndoButton provided the strongest ACL femoral fixation with significantly less graft-implant elongation and significantly higher failure loads. It was also shown in a porcine model that implants on the anterior cortical surface perform better than those on the lateral surface. Increased cortical thickness, in the range tested, was not associated with improved implant performance in the porcine model. CLINICAL RELEVANCE The EndoButton provided the best ACL femoral fixation of the devices tested.

Thumb Interphalangeal Joint Extension By the Extensor Pollicis Brevis: Association With a Subcompartment and de Quervain's Disease

PURPOSE First dorsal compartment anatomy was analyzed for the presence of a separate compartment for the extensor pollicis brevis (EPB) tendon and the ability of the EPB to extend the thumb interphalangeal (IP) joint in order to determine if these characteristics were associated with each other, and with de Quervains disease. METHODS Two groups were studied: (1) 90 cadaver wrists, 28 to 89 years, 38 male and 52 female specimens; and (2) 143 patient wrists, 21 to 82 years, 18 men and 125 women, in which the first dorsal compartment was released for treatment of de Quervains disease. RESULTS The EPB was in a separate compartment in 102 of 143 of the surgical group and 18 of 90 of the cadaver group. The EPB was able to extend the IP joint in 56 of 143 of the surgical group and 19 of 90 of the cadaver group. When the EPB was able to extend the IP joint, it was in a subcompartment in 49 of 56 of the surgical group and 9 of 19 of the cadaver group. When the EPB was able to produce IP extension in the cadaver group, it was inserted on the distal phalanx or the extensor hood. CONCLUSIONS In a substantial number of people undergoing surgery for de Quervains disease and in cadavers, the EPB can extend the thumb IP joint. When it does, particularly in patients with de Quervains disease, it is likely to reside in a subcompartment of the first dorsal compartment. The incidences of a subcompartment for the EPB and the ability of the EPB to extend the thumb IP joint were higher in the de Quervains patient population than in the cadaver group.

Effects of extensor pollicis longus transposition and extensor indicis proprius transfer to extensor pollicis longus on thumb mechanics.

PURPOSE The spatial relationship of the extensor pollicis longus (EPL) to the thumb carpometacarpal (CMC) joint may be altered by its transposition from the third dorsal wrist compartment and by subcutaneous extensor indicis proprius (EIP) to EPL tendon transfer. Changes in tendon position could alter thumb function. This study examined changes in the EPL adduction moment arm after EPL tendon transposition from its extensor compartment or EIP transfer. METHODS The EPL adduction moment arm at the thumb carpometacarpal joint was determined under 4 tendon conditions: (1) intact extensor pollicis longus, (2) transposed extensor pollicis longus, (3) extensor indicis proprius to extensor pollicis longus tendon transfer through an extensor retinacular pulley, and (4) extensor indicis proprius tendon transfer through a subcutaneous route. Each tendon condition was tested in 2 wrist positions: neutral and 40 degrees of flexion. RESULTS The wrist neutral/flexion moment arms for the 4 tendon conditions, in millimeters, were 9.2/7.3, 3.6/1.2, 8.3/5.1, and 4.8/1.0. CONCLUSIONS EPL transposition produces a significant decrease of its adduction moment arm at the thumb CMC joint, an effect exacerbated by wrist flexion. The moment arm mechanics of the pulley and subcutaneous EIP tendon transfer resemble those of the intact and transposed EPL, respectively. Diminution of the adduction moment arm could impair thumb function, especially adduction.

Use of a Torque-Range-of-Motion Device for Objective Differentiation of Diabetic from Normal Feet in Adults

Background: The ability of the foot and ankle complex to act as an energy absorber is reflected in its viscoelastic properties. The Torque-Range-of-Motion (TROM) device was designed to provide an effective objective assessment of foot and ankle passive mechanical function. The hypothesis of this study was that mechanical parameters derived from passive TROM curves of otherwise normal feet of adults with diabetes would be significantly different from those of adults without diabetes. Methods: The TROM device is a single-degree-of-freedom hinge transducer system that is manually rotated through plantarflexion and dorsiflexion. The device was rotated manually with the muscles relaxed during a 50-second data acquisition period. A strain gauge provided the torque signal and a precision single-turn potentiometer provided plantarflexion-dorsiflexion angle to a two-channel portable data acquisition system. With the TROM device connected to a computer, input for instantaneous torque and range of motion was acquired and displayed as angle (degrees) versus torque (Newton-meters) on an output screen. The period provided sufficient data to average 16 to 20 cycles of motion. The study included 41 feet in adults without diabetes and 42 age-matched feet in adults with diabetes but no known foot problems. Results: For a probability level of .0001 there were significant differences in hysteresis area (normal: 91.1 ± 46.9 Nm-deg and diabetic: 161.7 ± 65.7 Nm-deg) and both dorsiflexion (normal: 0.4 ± 0.1 Nm/deg and diabetic: 0.9 ± 0.3 Nm/deg) and plantarflexion stiffness (normal: 0.3 ± 0.1 Nm/deg and diabetic: 0.7 ± 0.3 Nm/deg). Conclusions: The feet of adults with diabetes absorb more energy during cyclic motion (thus must dissipate more energy per cycle) and are stiffer in the terminal regions (where muscle-tendon-ligament properties prevail) than are the feet of adults without diabetes. These results suggest that this passive TROM method may be a sensitive, objective measurement of the viscoelastic properties of the foot and ankle, which may be an early indicator of diabetic patients who are at risk for the development of foot problems.