Purpose: Aseptic loosening is one of the leading causes of failure in total elbow arthroplasty. It is logical to postulate that incorrect implant positioning and alignment may lead to excessive loading and wear which can induce the loosening cascade. However, the effect of implant malalignment on wear inducing loads in the elbow is not yet known. This in-vitro study determined the effect of anterior malpositioning, and varus-valgus (VV) and internal-external (IE) malrotations on humeral stem loading in total elbow arthroplasty.

Method: The humeral, ulnar, and radial components of a linked total elbow arthroplasty were optimally positioned using computer navigation in eight cadaveric elbows, mounted in a load/motion control elbow simulator (age 75yrs, range 42–93; 5 male). A modular, humeral component was employed to generate implant malpositioning errors of ±6° VV, ±8° IE, and 5mm anterior. The implant was instrumented with strain gauges to quantify VV and IE bending loads during elbow flexion with the forearm in supination. Load output was combined using a sum-of-squares technique. Passive flexion was performed with the arm in the varus and valgus orientations; passive and active flexion were performed with the arm in the vertical orientation.

Results: With the arm (humerus) in the vertical orientation, bending loads increased between 418Nmm and 1618Nmm for all malaligned implant positions (p< 0.05). Passive flexion (1354±859Nmm) produced higher resultant loads for the optimally positioned implant than active (819±891Nmm) flexion (p< 0.05). Although it varied during flexion, loading with the arm in varus (2928±1273Nmm) or valgus (2494±743Nmm) orientations resulted in up to a three-fold increase in loading when compared to the vertical orientation (p< 0.01).

Conclusion: These data demonstrate that humeral component malpositioning increases loading in the implant, however further studies are required to determine the long term effect on polyethylene wear and component loosening. Prosthesis designs that replicate the native flexion-extension axis and make use of sophisticated instrumentation or computer assistance to achieve precise positioning during implantation should lead to improved arthroplasty durability. Also, loading was higher with the arm in varus or valgus orientations, suggesting that patients should avoid activities post-operatively that require their elbow to be positioned in this way.

Purpose: Ligaments and osseous constraints are the only static stabilizers in a healthy elbow. Following arthroplasty, the use of semi-constrained, or linked, implants provides a potential third static stabilizer. However, this constraint may increase loading on the prosthesis, and hence accelerate polyethylene wear. The presence of competent collateral ligaments and the radial head would be expected to improve elbow stability and decrease loading on the ulnohumeral articulation. This in vitro study determined the effects of the collateral ligaments, radial head, and implant linkage on kinematics and wear-inducing loads in total elbow arthroplasty.

Method: Eight cadaveric upper extremities (age 73.5yrs; 5 male), were tested using an elbow motion simulator. Humeral, ulnar, and radial components of an elbow arthroplasty were positioned using a computer-assisted technique. Varus-valgus and internal-external bending loads were measured during flexion using an instrumented humeral component. A tracking receiver attached to the ulna recorded its position during active and passive flexion in the vertical orientation, and passive flexion in the varus and valgus orientations. Kinematics and loading were measured with and without implant linkage, with an intact, resected and replaced radial head, and before and after sectioning of the collateral ligaments.

Results: There were no differences in the bending loads with the arm in the vertical orientation regardless of the status of the ligaments, radial head or implant linkage (p> 0.2). Radial head excision produced an increase in valgus angulation of the ulna (6.7±6.4°) but did not influence bending loads in the vertical orientation (p< 0.05). Loading was lowest with the unlinked implant, and with ligaments and radial head intact, with the arm in the valgus (1065±466Nmm) (p< 0.01) and varus (1333±698Nmm) (p< 0.05) orientations.

Conclusion: Our results show that the radial head is an important valgus stabilizer for the prosthesis employed in this investigation. Linkage of the articulation increases implant loading during passive flexion with the arm in the varus and valgus orientations, which may increase implant wear. This suggests that, when using prostheses of this design, linkage of the articulation may be unnecessary if adequate bone stock and ligaments are available, whilst preserving or repairing the collateral ligaments and preserving or replacing the radial head.

This in-vitro study evaluated the influence of ligament tensioning and the effectiveness of lateral collateral ligament (LCL) repair using transosseous sutures on the initial kinematics and stability of the elbow.

Six fresh upper-extremities were mounted in a motion simulator with tracking system, which enabled both passive and simulated active elbow flexion. The intact elbow was tested then the LCL was sectioned from its humeral origin and repaired with a transosseous suture technique. Locking sutures were placed in the LCL and passed through a humeral bone tunnel entering at the centre of curvature of the capitellum with exit holes in the lateral epicondyle. An actuator pulled on the sutures to achieve 20, 40 and 60 N of LCL repair tension and the sutures were then secured. The dependent variable of this study was the motion pathways of the ulna relative to the humerus. The data were analyzed using a two-way, repeated-measures ANOVA with relevant post-hoc paired t-tests.

With the arm oriented in the horizontal position under varus gravity loading, the repairs tracked in greater valgus than the intact LCL regardless of the repair tension. The larger the initial repair tension, the more the elbows tracked in valgus. Initial tension of 60 N was statistically different than the intact LCL with the forearm in pronation (p=0.04). Both the 40 and 60 N initial tensions were statistically different than the intact LCL with the forearm in supination (p< 0.01).

Repair of the LCL using transosseous sutures effectively restores the varus stability of the elbow. The initial tension of LCL repairs affects the kinematics of the elbow, with a tendency to over-tighten the ligament and pull the elbow into valgus. These data suggest that acute repair of the LCL should be performed using a transosseous suture technique, and that a tension of 20N or perhaps less is sufficient to restore stability.

A primary mode of failure for total elbow arthroplasty is osteolysis caused by wear debris. Loading of the polyethylene components by off-axis bearing loads is the likely cause of this debris. Load transfer at the elbow is affected by many factors, including the state of the radial head. New implant designs provide the option to use the intact, resected, or implant reconstructed radial head. However, the effect of the radial head state on stability and loading has not yet been investigated in these new implant designs.

We postulated that the presence of the native or prosthetic radial head would reduce the wear-inducing loading patterns experienced by the humeral component and improve joint stability compared to when the radial head is resected.

Seven cadaveric upper extremities, amputated at the mid humerus, were tested in a joint motion simulator equipped with an electromagnetic tracking system to quantify motion. Simulated active flexion was tested with the arm in the dependent position. Passive elbow flexion was conducted with the arm in the varus and valgus gravity-loaded orientations. After testing the intact elbow, the collateral ligaments were sectioned and a linked Latitude ulno-humeral joint replacement was performed (Tornier, Stafford, TX). The humeral component was instrumented with strain gauges for measuring varus-valgus bending and internal-external torsion. Ulno-humeral kinematics and humeral component loading were measured when the radial head was intact, resected, and following radial head arthroplasty.

An increase in varus-valgus laxity was noted following replacement of the ulno-humeral joint with the prosthesis (p< 0.05). There was no difference in joint laxity between the intact radial head, radial head excision or radial head arthroplasty (p> 0.05). Torsion moments increased, while bending loads decreased in the humeral component following radial head excision and were restored following radial head arthroplasty (p< 0.05).

No significant effect of radial head state on varus-valgus joint laxity was observed for the linked ulno-humeral prosthesis. In the absence of collateral ligaments, the observed post-operative increase in varus-valgus laxity can be attributed to the difference in laxity between the native joint and the articular components of the linked implant. Load transfer was altered by radial head excision, which may affect the magnitude of bearing wear and the incidence of aseptic loosening. Further studies are required to determine whether these changes in load transfer influence wear of the polyethylene components or implant loosening.