The Relationship Between the Tensile and the Torsional Properties of the Native Scapholunate Ligament and Carpal Kinematics

PURPOSE

The purpose of this exploratory study was to examine the relationship between the tensile and the torsional properties of the native scapholunate interosseous ligament (SLIL) and kinematics of the scaphoid and lunate of an intact wrist during passive radioulnar deviation.

METHODS

Eight fresh-frozen cadaveric specimens were transected at the elbow joint and loaded into a custom jig. Kinematic data of the scaphoid and lunate were acquired in a simulated resting condition for 3 wrist positions-neutral, 10° radial deviation, and 30° ulnar deviation-using infrared-emitting rigid body trackers. The SLIL bone-ligament-bone complex was then resected and loaded on a materials testing machine. Specimens underwent cyclic torsional and tensile testing and SLIL tensile and torsional laxity were evaluated. Correlations between scaphoid and lunate rotations and SLIL tensile and torsional properties were determined using Pearson correlation coefficients.

RESULTS

Ulnar deviation of both the scaphoid and the lunate were found to decrease as the laxity of SLIL in torsion increased. In addition, the ratio of lunate flexion-extension to radial-ulnar deviation was found to increase with increased SLIL torsional rotation.

CONCLUSIONS

Our findings support the theory that there is a relationship between scapholunate kinematics and laxity at the level of the interosseous ligaments.

CLINICAL RELEVANCE

Laxity and, specifically, the tensile and torsional properties of an individual's native SLIL should guide reconstruction using a graft material that more closely replicates the individual's native SLIL properties.

Ankle joint contact loads and displacement in syndesmosis injuries repaired with Tightropes compared to screw fixation in a static model

BACKGROUND

The effect of syndesmotic fixation on restoration of pressure mechanics in the setting of a syndesmotic injury is largely unknown. The purpose of this study is to examine the contact mechanics of the tibiotalar joint following syndesmosis fixation with screws versus a flexible fixation device for complete syndesmotic injury.

METHODS

Six matched pairs of cadaveric below knee specimens were dissected and motion capture trackers were fixed to the tibia, fibula, and talus and a pressure sensor was placed in the tibiotalar joint. Each specimen was first tested intact with axial compressive load followed by external rotation while maintaining axial compression. Next, syndesmotic ligaments were sectioned and randomly assigned to repair with either two TightRopes® or two 3.5 mm cortical screws and the protocol was repeated. Mean contact pressure, peak pressure, reduction in contact area, translation of the center of pressure, and relative talar and fibular motion were calculated. Specimens were then cyclically loaded in external rotation and surviving specimens were loaded in external rotation to failure.

RESULTS

No differences in pressure measurements were observed between the intact and instrumented states during axial load. Mean contact presure relative to intact testing was increased in the screw group at 5 Nm and 7.5 Nm torque. Likewise, peak pressure was increased in the TightRope group at 7.5 Nm torque. There was no change in center of pressure in the TightRope group at any threshold; however, at every threshold tested there was significant medial and anterior translation in the screw group relative to the intact state.

CONCLUSION

Either screws or TightRope fixation is adequate with AL alone. With lower amounts of torque, the TightRope group appears to have contact and pressure mechanics that more closely match native mechanics.

Tensile and Torsional Structural Properties of the Native Scapholunate Ligament

PURPOSE

The ideal material for reconstruction of the scapholunate interosseous ligament (SLIL) should replicate the mechanical properties of the native SLIL to recreate normal kinematics and prevent posttraumatic arthritis. The purpose of our study was to evaluate the cyclic torsional and tensile properties of the native SLIL and load to failure tensile properties of the dorsal SLIL.

METHODS

The SLIL bone complex was resected from 10 fresh-frozen cadavers. The scaphoid and lunate were secured in polymethylmethacrylate and mounted on a test machine that incorporated an x-y stage and universal joint, which permitted translations perpendicular to the rotation/pull axis as well as nonaxial angulations. After a 1 N preload, specimens underwent cyclic torsional testing (±0.45 N m flexion/extension at 0.5 Hz) and tensile testing (1-50 N at 1 Hz) for 500 cycles. Lastly, the dorsal 10 mm of the SLIL was isolated and displaced at 10 mm/min until failure.

RESULTS

During intact SLIL cyclic torsional testing, the neutral zone was 29.7° ± 6.6° and the range of rotation 46.6° ± 7.1°. Stiffness in flexion and extension were 0.11 ± 0.02 and 0.12 ± 0.02 N m/deg, respectively. During cyclic tensile testing, the engagement length was 0.2 ± 0.1 mm, the mean stiffness was 276 ± 67 N/mm, and the range of displacement was 0.4 ± 0.1 mm. The dorsal SLIL displayed a 0.3 ± 0.2 mm engagement length, 240 ± 65 N/mm stiffness, peak load of 270 ± 91 N, and displacement at peak load of 1.8 ± 0.3 mm.

CONCLUSIONS

We report the torsional properties of the SLIL. Our novel test setup allows for free rotation and translation, which reduces out-of-plane force application. This may explain our observation of greater dorsal SLIL load to failure than previous reports.

CLINICAL RELEVANCE

By matching the natural ligament with respect to its tensile and torsional properties, we believe that reconstructions will better restore the natural kinematics of the wrist and lead to improved outcomes. Future clinical studies should aim to investigate this further.

Association of Lunate Morphology With Carpal Instability in Scapholunate Ligament Injury

BACKGROUND

We examined the relationship between lunate morphology (type 1 without a medial facet; type II with a medial facet) and dorsal intercalated segmental instability (DISI) in patients with scapholunate ligament injuries. We tested the primary null hypothesis that there is no relationship between lunate morphology and development of DISI. Secondary analysis compared the agreement of classifying lunate morphology based on the presence of a medial lunate facet, capitate-to-triquetrum (CT) distance, and magnetic resonance imaging (MRI).

METHODS

We performed a retrospective chart review of patients with known scapholunate ligament injuries from 2001 to 2016. Posterior-anterior radiographs and MRI, when available, were evaluated. CT distances were measured as a secondary classification method. DISI and scapholunate instability were determined as radiolunate angle >15° and scapholunate angle >60°, respectively. Differences between groups were determined using chi-square analysis with significance set at P < .05. Agreement between plain radiographs, MRI, and CT distance was calculated using the kappa statistic.

RESULTS

Our search found 58 of 417 patients who met inclusion criteria; 41 of 58 had type II and 17 of 58 had type I lunates. There was no significant difference between groups in regard to DISI or scapholunate instability. Subanalysis using MRI alone or correcting any discrepancy between plain film and MRI classification, using MRI as the standard, found no difference between groups in regard to DISI or scapholunate instability.

CONCLUSIONS

In patients with scapholunate ligament injuries, there are no differences in the development of DISI or scapholunate instability between patients with type I and type II lunates.

Anatomy and Biomechanics of the Finger Proximal Interphalangeal Joint

A complete understanding of the normal anatomy and biomechanics of the proximal interphalangeal joint is critical when treating pathology of the joint as well as in the design of new reconstructive treatments. The osseous anatomy dictates the principles of motion at the proximal interphalangeal joint. Subsequently, the joint is stabilized throughout its motion by the surrounding proximal collateral ligament, accessory collateral ligament, and volar plate. The goal of this article is to review the normal anatomy and biomechanics of the proximal interphalangeal joint and its associated structures, most importantly the proper collateral ligament, accessory collateral ligament, and volar plate.

Cost minimization analysis of the treatment of distal radial fractures in the elderly

AIMS

The aim of this study was to test the null hypothesis that there is no difference, from the payer perspective, in the cost of treatment of a distal radial fracture in an elderly patient, aged > 65 years, between open reduction and internal fixation (ORIF) and closed reduction (CR).

MATERIALS AND METHODS

Data relating to the treatment of these injuries in the elderly between January 2007 and December 2015 were extracted using the Humana and Medicare Advantage Databases. The primary outcome of interest was the cost associated with treatment. Secondary analysis included the cost of common complications. Statistical analysis was performed using a non-parametric t-test and chi-squared test.

RESULTS

Our search yielded 8924 patients treated with ORIF and 5629 patients treated with CR. The mean cost of an uncomplicated ORIF was more than a CR ($7749 versus $2161). The mean additional cost of a complication in the ORIF group was greater than in the CR group ($1853 versus $1362).

CONCLUSION

These findings show that there are greater payer fees associated with ORIF than CR in patients aged > 65 years with a distal radial fracture. CR may be a higher-value intervention in these patients. Cite this article: Bone Joint J 2018;100-B:205-11.

Treatment Trends in Older Adults With Midshaft Clavicle Fractures

PURPOSE

We present a retrospective administrative claims database review examining the effect of recent literature supporting surgical clavicle fixation in a primarily young male population, on the treatment of midshaft clavicle fractures in patients older than 65 years. We tested the null hypothesis that there is no change in trends in surgical fixation of midshaft clavicle fractures in patients older than 65 years. Secondary analysis examined overall trends and trends based on sex.

METHODS

Data from 2007 to 2012 were extracted using the Medicare Standard Analytic File and Humana administrative claim databases contained within the PearlDiver Patient Records Database. Patients with clavicle shaft fractures and their treatments were identified by International Classification of Disease, Ninth Revision, and Current Procedural Terminology codes. The primary response variable was the proportion of surgical to nonsurgical cases per year, and explanatory variables included age and sex. Data were analyzed using a trend in proportions test with significance set at P less than .05.

RESULTS

A total of 32,929 patients with clavicle shaft fractures were identified. During the study period, the proportion of clavicle shaft fractures treated surgically in patients older than 65 years (2.4%-4.6%) and younger than 65 years (11.2%-16.4%) showed a significant increasing trend. When analyzed by both sex and age, there was also an increasing trend in the proportion of surgically treated males in the older than 65 years (3.3%-6.2%) and the younger than 65 years groups (10.9%-19.5%). Lastly, there was an increase in the proportion of surgically treated females older than 65 years (1.7%-3.4%) and younger than 65 years (12.1%-14.3%).

CONCLUSIONS

Our analysis demonstrates an overall increase in the proportion of surgically treated clavicle shaft fractures, including in the male and female population older than 65 years. In the setting of an aging population, future research evaluating possible benefits of surgical intervention in this population is needed prior to adopting this practice pattern.

TYPE OF STUDY/LEVEL OF EVIDENCE

II.

Cost Minimization Analysis of Ganglion Cyst Excision

PURPOSE

Cost minimization analysis can be employed to determine the least costly option when multiple treatments lead to equivalent outcomes. We present a cost minimization analysis from the payers' perspective, of the direct per patient cost of arthroscopic versus open ganglion cyst excision. We tested the null hypothesis that there is no difference in cost between the 2 procedures from the payer perspective.

METHODS

We utilized data from a private payer administrative claims database comprising 16 million individuals from 2007 to 2015. Using Current Procedural Terminology codes to identify open and arthroscopic ganglion excisions, we extracted demographic data and fees paid to providers and facilities for the procedure.

RESULTS

We identified 5,119 patients undergoing open ganglion cyst excision and 20 patients undergoing arthroscopic ganglion excision. The average cost of an open excision was significantly lower than an arthroscopic excision ($1,821 vs $3,668).

CONCLUSIONS

Surgical costs from arthroscopic ganglion excision are significantly more than open excision. This data can inform health systems participating in value-based models.

TYPE OF STUDY/LEVEL OF EVIDENCE

Economic and Decision Analysis IV.