Levi G. Sutton

Dynamic Biomechanical Evaluation of the Dorsal Intercarpal Ligament Repair for Scapholunate Instability

PURPOSE A variety of soft tissue surgical procedures have been developed for treatment of scapholunate dissociation. One reconstruction method, using the dorsal intercarpal ligament, has been used clinically with some success. The purpose of this study was to evaluate biomechanically use of the dorsal intercarpal ligament for static scapholunate dissociation. METHODS Eight cadaver wrists were tested in a wrist joint motion simulator. Each wrist was moved in continuous cycles of flexion-extension and radial-ulnar deviation. Kinematic data for the scaphoid and lunate were recorded for each wrist in the intact state, after the scapholunate interosseous, dorsal radiocarpal, and dorsal intercarpal ligaments were sectioned, and after reconstruction using the dorsal intercarpal ligament. RESULTS Ligamentous sectioning resulted in static scapholunate dissociation. Visually, the repair initially reduced the gap between the scaphoid and lunate, but within a few cycles of wrist motion, there were statistically significant increases in scaphoid flexion, scaphoid ulnar deviation, and lunate extension. In 6 arms, gapping between the scaphoid and lunate was observed. In 2 arms, a gap occurred and the repair also pulled out of the bone junction. CONCLUSIONS This study does not support the hypothesis that the dorsal intercarpal ligament repair alone will stabilize the scaphoid and lunate after scapholunate instability in the immediate postoperative period.

Morphology of the Cubital Tunnel: An Anatomical and Biomechanical Study With Implications for Treatment of Ulnar Nerve Compression

PURPOSE The purpose of this study is to provide a thorough understanding of the anatomy of the cubital tunnel and to outline specific anatomical parameters of the cubital tunnel retinaculum (CuTR) that might aid in the management of ulnar nerve problems. The hypotheses of this study are (1) that the nerve elongates with elbow flexion and (2) that the cross-sectional area of the cubital tunnel is inversely proportional to the degree of elbow flexion. METHODS Eleven fresh-frozen cadaver arms were dissected at the medial elbow. The CuTR was identified, and its thickness was measured. After excising the CuTR, we measured the elongation of the anterior and posterior aspects of the ulnar nerve, as well as the length of the CuTR origin/insertion, at increasing intervals of elbow flexion (15°, 30°, 45°, 90°, 120°, and 135°). Using 3-dimensional digitization technology, the surface of the cubital tunnel was recorded at 4 positions of elbow flexion (15°, 45°, 90°, and 135°) and analyzed to define the tunnel geometry. RESULTS The CuTR origin-to-insertion length and the ulnar nerve length both increased significantly with increasing flexion angle. Both lengths at 90°, 120°, and 135° of elbow flexion were greater than at 15° or 30°. The cubital tunnel area was significantly less at 135° compared to either 45° or 90° of flexion. There was a linear relationship between the cubital tunnel area of the different arms with the corresponding nerve cross-sectional area when measured at the level of the epicondyle and when the arm was at 90° of elbow flexion. CONCLUSIONS The CuTR begins to stretch at 60° of flexion and continues to stretch with increasing flexion. Similarly, the ulnar nerve is more taut in flexion. The area within the cubital tunnel decreases beyond 90° of elbow flexion. CLINICAL RELEVANCE Understanding the dynamic anatomical relationships of the cubital tunnel might help in the safe treatment of cubital tunnel syndrome when using minimally invasive techniques and instrumentation.

4-Corner Arthrodesis and Proximal Row Carpectomy: A Biomechanical Comparison of Wrist Motion and Tendon Forces

PURPOSE Controversy exists as to whether a proximal row carpectomy (PRC) is a better procedure than scaphoid excision with 4-corner arthrodesis for preserving motion in the painful posttraumatic arthritic wrist. The purpose of this study was to determine how the kinematics and tendon forces of the wrist are altered after PRC and 4-corner arthrodesis. METHODS We tested 6 fresh cadaver forearms for the extremes of wrist motion and then used a wrist simulator to move them through 4 cyclic dynamic wrist motions, during which time we continuously recorded the tendon forces. We repeated the extremes of wrist motion measurements and the dynamic motions after scaphoid excision with 4-corner arthrodesis, and then again after PRC. We analyzed extremes of wrist motion and the peak tendon forces required for each dynamic motion using a repeated measures analysis of variance. RESULTS Wrist extremes of motion significantly decreased after both the PRC and 4-corner arthrodesis compared with the intact wrist. Wrist flexion decreased on average 13° after 4-corner arthrodesis and 12° after PRC. Extension decreased 20° after 4-corner arthrodesis and 12° after PRC. Four-corner arthrodesis significantly decreased wrist ulnar deviation from the intact wrist. Four-corner arthrodesis allowed more radial deviation but less ulnar deviation than the PRC. The average peak tendon force was significantly greater after 4-corner arthrodesis than after PRC for the extensor carpi ulnaris during wrist flexion-extension, circumduction, and dart throw motions. The peak forces were significantly greater after 4-corner arthrodesis than in the intact wrist for the extensor carpi ulnaris during the dart throw motion and for the flexor carpi ulnaris during the circumduction motion. The peak extensor carpi radialis brevis force after PRC was significantly less than in the intact wrist. CONCLUSIONS The measured wrist extremes of motion decreased after both 4-corner arthrodesis and PRC. Larger peak tendon forces were required to achieve identical wrist motions with the 4-corner arthrodesis compared with the intact wrist. We observed smaller forces for the PRC. CLINICAL RELEVANCE These results may help explain why PRC shows early clinical improvement, yet may lead to degenerative arthritis.

Scaphoid and lunate translation in the intact wrist and following ligament resection: A cadaver study

PURPOSE To determine the amount of scaphoid and lunate translation that occurs in normal cadaver wrists during wrist motion, and to quantify the change in ulnar translation when specific dorsal and volar wrist ligaments were sectioned. METHODS We measured the scaphoid and lunate motion of 37 cadaver wrists during wrist radioulnar deviation and flexion-extension motions using a wrist joint motion simulator. We quantified the location of the centroids of the bones during each motion in the intact wrists and after sectioning either 2 dorsal ligaments along with the scapholunate interosseous ligament or 2 volar ligaments and the scapholunate interosseous ligament. RESULTS In the intact wrist, the scaphoid and lunate statistically translated radially with wrist ulnar deviation. With wrist flexion, the scaphoid moved volarly and the lunate dorsally. After sectioning either the dorsal or volar ligaments, the scaphoid moved radially. After sectioning the dorsal or volar ligaments, the lunate statistically moved ulnarly and volarly. CONCLUSIONS Measurable changes in the scaphoid and lunate translation occur with wrist motion and change with ligament sectioning. However, for the ligaments that were sectioned, these changes are small and an attempt to clinically measure these translations of the scaphoid and lunate radiographically may be limited. The results support the conclusion that ulnar translocation does not occur unless multiple ligaments are sectioned. Injury of more than the scapholunate interosseous ligament along with either the dorsal intercarpal and dorsal radiocarpal or the radioscaphocapitate and scaphotrapezial ligaments is needed to have large amounts of volar and ulnar translation.

Optimization of glenoid fixation in reverse shoulder arthroplasty using 3-dimensional modeling

BACKGROUND Reverse shoulder fixation complications may be related to how much glenoid bone is removed and how the fixation screws are located in the glenoid. The purpose of this study was to determine how much bone volume and surface area are lost with incremental reaming and to evaluate screw fixation. METHODS A contemporary reverse shoulder implant was virtually implanted into models of 6 different shoulders following initial and then after additional incremental reaming was performed. Changes in the glenoid bone surface area and volume available for fixation were statistically evaluated using repeated measures ANOVAs. RESULTS The total bone volume, the amount of reamed glenoid surface area available for an implant baseplate, and the actual amount of the glenoid in contact with a baseplate decreased with increasing amounts of reaming. With 5 mm of reaming, the total volume decreased by 2810 mm(3), the reamed glenoid surface area decreased by 28%, and the amount of the glenoid in contact with the baseplate decreased by 27%. The amount of engagement of anterior and posterior screws was much less than that of the superior and inferior screws. CONCLUSION Careful reaming of the glenoid surface is critical, because as little as 1 extra millimeter of bone removal decreases the amount of bone available for implant fixation. After reaming there may not be enough bone to accommodate anterior and posterior screws with the design used in this study.

Wrist Tendon Forces During Various Dynamic Wrist Motions

PURPOSE A common treatment of arthritis of the thumb carpometacarpal joint requires all or a portion of the flexor carpi radialis tendon (FCR) to be used as an interpositional graft. The purpose of this study was to examine the in vitro tendon forces in 6 wrist flexors and extensors to determine whether their force contribution changes during various dynamic wrist motions along with a specific application to the FCR. METHODS We tested 62 fresh-frozen cadaver wrists in a wrist joint motion simulator. During wrist flexion-extension, radioulnar deviation, dart throwing, and circumduction motions, the peak and average tendon forces were determined for the extensor carpi ulnaris, extensor carpi radialis brevis and longus, abductor pollicis longus, flexor carpi radialis, and flexor carpi ulnaris. RESULTS During a dart-throwing motion, the mean and peak FCR forces were statistically less than during the other 3 motions. Conversely, the mean and peak flexor carpi ulnaris forces were statistically greater during the dart-throwing motion than during the other 3 motions. CONCLUSIONS Patients who have undergone a surgical procedure in which all or a portion of the FCR has been harvested may experience a decrease in wrist strength with wrist motion, as the FCR tendon normally applies force during wrist motion. The motion least likely to be affected by such surgery is the dart-throwing motion when the force on the remaining FCR is minimized.

In vitro response of the natural cadaver knee to the loading profiles specified in a standard for knee implant wear testing

The purpose of this study was to examine how a natural knee responds to the inputs of a total knee replacement testing standard developed by the International Organization for Standardization (ISO). This load control standard prescribes forces to be used for wear testing of knee replacements independent of implant size or design. A parallel ISO standard provides wear testing inputs that are displacement based instead of force based. Eight fresh frozen cadaveric knees were potted and tested in a 6 degree of freedom knee simulator using the load-control standard. The resulting displacements during load-control testing were compared to the prescribed displacements of the ISO displacement standard. At half the tibial torque prescribed by the load standard there was three times more average internal tibial rotation (20.3 degrees) than is prescribed by the displacement standard (5.7 degrees). The AP motion resulting from load testing was much different than is specified by the displacement standard. All eight knees had anterior tibial translation with respect to the femur during swing phase while the displacement standard specifies posterior tibial displacement. The variation in these motions among knees and their difference from the ISO displacement standard may be one factor that explains why wear results of total knee replacements based on ISO load or displacement testing frequently do not agree with each other or with clinical retrievals.

Knee Medial Compartment Contact Pressure Increases With Release of the Type I Anterior Intermeniscal Ligament

Background The anterior intermeniscal ligament of the knee is at risk during knee arthroscopy, anterior cruciate ligament reconstruction, and tibial nail insertion. Hypothesis Release of the anterior intermeniscal ligament, in knees with type I ligaments, will result in altered contact pressures in the medial compartment. Study Design Controlled laboratory study. Methods Five fresh-frozen human cadaveric knees with intact type I anterior intermeniscal ligaments were chosen for testing in a modified MTS machine from 0° to 60° of flexion under 2 conditions: (1) intact and (2) after sharp sectioning of the anterior intermeniscal ligament. Measurements were made using inframeniscal contact pressure sensors covering the medial compartment. Poststudy analysis was done in 10° increments between 0° and 60° of flexion, looking at peak contact pressure and the amount of contact area seeing pressure. Results Sectioning of the anterior intermeniscal ligament caused a statistically significant increase in the peak pressure at 20°, 30°, 40°, and 50° of knee flexion. The largest change occurred at 40° of knee flexion, when the peak pressure increased by 27.5% (3.68 MPa to 4.69 MPa). Contact area decreased, although this difference was not statistically significant. Conclusion Release of the anterior intermeniscal ligament results in increased peak contact pressures in the medial compartment of the knee. Clinical Relevance Care should be taken to avoid sacrifice of this ligament during surgery.

Proximal Row Carpectomy: Role of a Radiocarpal Interposition Lateral Meniscal Allograft

PURPOSE The purpose of this study was to determine whether use of a lateral meniscal interposition allograft combined with proximal row carpectomy would reduce the peak joint contact pressures and increase the contact area when compared with proximal row carpectomy alone. METHODS Six cadaver wrists were cyclically moved through flexion-extension and radioulnar deviation ranges of motion. Joint contact pressure was measured with the carpus intact, after proximal row carpectomy, and after insertion of a lateral meniscal allograft. Contact pressure data were also collected with the wrist in 5 static positions. RESULTS Proximal row carpectomy caused statistically greater peak pressures and smaller contact areas when compared with the intact wrist. Insertion of the allograft statistically restored the pressures and areas to that observed in the intact wrist. CONCLUSIONS These results support the clinical trial of a lateral meniscal interposition allograft in patients with contraindications for proximal row carpectomy, such as pre-existing arthritis in the capitate head or lunate facet of the radius.

Does glenoid baseplate geometry affect its fixation in reverse shoulder arthroplasty

BACKGROUND The effect of glenoid baseplate geometry has not been studied as it pertains to reverse shoulder arthroplasty. The purpose of this study was to compare 2 baseplate designs whose major difference is being either a flat backed design or a convex baseplate, with regard to their bone interface area, screw engagement, and bone volume removed using 3-dimensional modeling. METHODS Three-dimensional models of 6 scapulae were used to virtually implant models of a flat backed and a convex backed glenoid baseplate. Additional reaming was performed in 1 mm increments, up to 5 mm, and the amount of baseplate screw engagement was calculated at each increment. Statistical differences between flat and convex implants were calculated. RESULTS Insertion of the convex baseplate required statistically greater removal of bone as compared to the flat baseplate (P = .003). No statistical changes in total area were observed with reaming of the glenoid for the convex baseplate (P > .095). However, for the flat baseplate, 1 mm of reaming caused a statistical decrease in area available for fixation. The amount of total bone area in contact with a convex baseplate was statistically greater than with a flat baseplate (P = .004). The amount of screw engagement was statistically less with the convex baseplate, compared to the flat (P = .026). DISCUSSION A convex backed glenoid baseplate can improve the contact surface area at the bone implant interface as compared to a flat backed design. However, better screw engagement and less bone volume removed during reaming favors a flat backed design, particularly when adequate bone-implant contact cannot be achieved.