Effect of Radiocapitellar Joint Over/Under Stuffing on Elbow Joint Contact Pressure.

PURPOSE: Comminuted radial head fractures are commonly treated by surgical resection or replacement with a prosthesis. A potential problem with radial head replacement is overlengthening of the radial neck ("overstuffing" of the radial head), which has been shown to affect both ulnohumeral kinematics and radiocapitellar pressures. We hypothesized that an overstuffed radial head prosthesis increases capitellar pressure and reduces coronoid pressure. METHODS: Seven human cadaveric elbows were prepared on a custom-designed apparatus simulating stabilizing muscle loads, and passively flexed from 0° to 90° under gravity valgus torque while joint contact pressures were measured. Each elbow was tested sequentially with different neck lengths, starting with the intact specimen followed by insertion of understuffed (-2 mm), standard-height (0 mm), and overstuffed (+2 mm) radial head prostheses in neutral forearm rotation, 40° pronation, and 40° supination positions, respectively. RESULTS: Capitellar mean contact pressures significantly increased after insertion of an overstuffed radial head prosthesis. In valgus position with neutral forearm rotation, capitellar mean contact pressure on the joint with an intact radial head averaged 227 ± 70 kPa. Insertion of understuffed, standard-height, and overstuffed radial head prostheses changed the mean contact pressures to 152 ± 76 kPa, 212 ± 68 kPa, and 491 ± 168 kPa, respectively. The overstuffed radial head group had significantly lower whole coronoid mean contact pressures (153 ± 56 kPa) compared with the intact (390 ± 138 kPa) and standard-height (376 ± 191 kPa) radial head groups. CONCLUSIONS: An increase in radial prosthesis height significantly increases capitellar contact pressures and reduces coronoid contact pressures. CLINICAL RELEVANCE: Restoration of the anatomic radial head height is critical when performing radial head arthroplasty to maintain normal joint biomechanics. Elevated capitellar contact pressures can potentially lead to pain and early degenerative changes.

Advantages of CT Versus MRI for Preoperative Assessment of Osteochondritis Dissecans of the Capitellum.

BACKGROUND: Magnetic resonance imaging (MRI) is considered to be the gold standard for imaging of osteochondritis dissecans (OCD). PURPOSE/HYPOTHESIS: The purpose was to determine the additional value of a preoperative computed tomography (CT) scan in adolescent patients with capitellar OCD of the elbow. Consistent with the fact that OCD is a lesion involving the subchondral bone, the hypothesis was that CT would be superior to MRI for imaging OCD of the capitellum. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 3. METHODS: All patients being treated surgically for an OCD of the capitellum between 2006 and 2016 at one institution were reviewed for preoperative imaging. A total of 28 patients met the inclusion criteria. Corresponding MRI and CT scans were compared retrospectively. Multiple parameters were recorded, with special emphasis on OCD lesion size, fragmentation, and tilt as well as joint surface integrity, loose bodies, and osteophytes. RESULTS: The OCD lesions were best seen on CT scans, whereas MRI T1-weighted images overestimated and T2-weighted images underestimated the size of defects. A subchondral fracture nonunion was found on CT scans in 18 patients, whereas this was seen on MRI T1-weighted images in only 2 patients (P < .001) and MRI T2-weighted images in 4 patients (P < .001). Fragmentation of the OCD fragment was found on CT scans in 17 patients but on MRI scans in only 9 patients (P = .05). Osteophytes as a sign of secondary degenerative changes were seen on CT scans in 24 patients and were seen on MRI scans in 15 patients (P = .02). Altogether, only 51 of 89 secondary changes including loose bodies, effects on the radial head and ulnohumeral joint, and osteophytes that were seen on CT scans were also seen on MRI scans (P = .002). CONCLUSION: OCD fragmentation and secondary changes were more often diagnosed on CT. These factors indicate OCD instability or advanced OCD stages, which are indications for surgery. In an adolescent who is considered at risk for OCD (baseball, gymnastics, weightlifting, tennis) and who has lateral elbow joint pain with axial or valgus load bearing, CT is our imaging modality of choice for diagnosing and staging OCD of the capitellum.

Effect of incremental increase in radial neck height on coronoid and capitellar contact pressures.

BACKGROUND: Over-lengthening of the radial neck has been shown to affect ulnohumeral kinematics and has been proposed to affect radiocapitellar pressures. We hypothesized that an incremental increase in radial neck height increases the capitellar contact pressure and reduces the coronoid contact pressure. Knowledge of the effects of over-lengthening is clinically important in preventing pain and degenerative changes due to overstuffing. METHODS: Six human cadaveric elbows were prepared on a custom-designed apparatus simulating muscle loads and passive flexion from 0° to 90° under gravity valgus torque while measuring joint contact pressures in this biomechanical study. Each elbow was tested sequentially starting with the intact specimen followed by insertion of a radial head prosthesis with 0, +2, and +4 mm of radial neck height, respectively. RESULTS: Capitellar mean contact pressures significantly increased after insertion of +2 and +4 mm radial head prostheses (p < 0.03). The capitellar mean contact pressure with a 0 mm radial head prosthesis was 97 KPa. Insertion of +2 mm and +4 mm radial heads increased mean contact pressures to 391 KPa (p = 0.001) and 619 KPa (p = 0.001), respectively, with 90° of elbow flexion. DISCUSSION: Increasing radial prosthesis height by 2 mm significantly increases capitellar contact pressures and reduces coronoid contact pressures.

Response of the Injured Tendon to Growth Factors in the Presence or Absence of the Paratenon.

BACKGROUND: The paratenon is important for Achilles tendon healing. There is much interest in the use of exogenous growth factors (GFs) as potential agents for accelerating the healing of damaged Achilles tendons. PURPOSE/HYPOTHESIS: The present study used a rat model to study the responses of the injured Achilles tendon to GFs in the presence or absence of the paratenon. The hypothesis was that responses of the injured tendon to GFs would be lower in the absence of a paratenon. STUDY DESIGN: Controlled laboratory study. METHODS: A 4-mm defect was created in the right Achilles tendon of 60 skeletally mature rats, which were treated with a validated combination of GFs (bFGF, BMP-12, and TGF-ß1). Animals were randomly assigned to the intact paratenon (IP) group or resected paratenon (RP) group. Healing was studied anatomically, mechanically, and histologically after 1, 2, and 4 weeks. RESULTS: IP tendons showed improved healing compared with RP tendons. IP tendons were significantly stronger (32.2 N and 48.9 N, respectively) than RP tendons (20.1 N and 31.1 N, respectively) after 1 and 2 weeks. IP tendons did not elongate as much as RP tendons and had greater cross-sectional areas (18.0 mm2, 14.4 mm2, and 16.4 mm2, respectively) after 1, 2, and 4 weeks compared with RP tendons (10.5 mm2, 8.4 mm2, and 11.9 mm2, respectively). On histology, earlier collagen deposition and parallel orientation of fibrils were found for IP tendons. CONCLUSION: The paratenon is essential for efficient Achilles tendon healing. Healing with GFs in this Achilles tendon defect model was superior in the presence of the paratenon. CLINICAL RELEVANCE: Biological approaches to tendon engineering using GFs are in vogue and have been shown to improve healing of the rat Achilles tendon, most likely by inducing progenitor cells located within the paratenon. Clinically, resection or incision of the paratenon has been proposed for wound closure. Our data demonstrate the fundamental importance of the paratenon, which therefore should be preserved during Achilles tendon repair, especially if augmented with products such as platelet-rich plasma or autologous conditioned serum that are rich in GFs.

Effect of radiocapitellar Achilles disc arthroplasty on coronoid and capitellar contact pressures after radial head excision.

BACKGROUND: Long-term radiographic arthritis has been commonly reported after radial head excision. Concern over radial head arthroplasty may arise in certain situations including capitellar arthritis, radiocapitellar malalignment, and in young and active patients. We hypothesized that radial head excision increases coronoid contact pressures, which may at least be partially reduced by radiocapitellar Achilles tendon disc arthroplasty. METHODS: Coronoid and capitellar contact pressure was measured on 6 human cadaveric elbows on a custom-designed gravity-valgus simulator under passive flexion from 0° to 90°. Sequential testing, starting with the intact specimen, resection of the radial head, and finally, radiocapitellar Achilles tendon disc arthroplasty were performed on each specimen. RESULTS: Mean contact pressure of the coronoid significantly increased after radial head excision (P < .0001) and significantly improved after Achilles disc arthroplasty (P < .0001). The pressure difference was most pronounced on the lateral coronoid. From 15° to 85° of elbow flexion, mean contact pressures on the lateral coronoid were 291 kPa and 476 kPa before and after radial head excision, respectively (P < .0001). Achilles disc arthroplasty significantly lowered coronoid contact pressures to 385 kPa (P = .002); however, they remained significantly higher than those in the intact radial head group (P = .0009). CONCLUSIONS: Radial head resection increases contact pressure in the coronoid, especially the lateral coronoid. This study showed that radiocapitellar Achilles disc arthroplasty significantly improves contact pressures on the coronoid after radial head resection. Achilles disc arthroplasty could be considered in patients who are not candidates for radial head arthroplasty.

Unacceptable failure of hemiarthroplasty combined with biological glenoid resurfacing in the treatment of glenohumeral arthritis in the young.

BACKGROUND: Treatment of glenohumeral osteoarthritis in young patients is challenging. Total shoulder arthroplasty reliably addresses pain and dysfunction but compromises glenoid bone stock. Various efforts have been made to avoid a prosthetic glenoid component or to prevent glenoid erosion after hemiarthroplasty. Capsular interposition, meniscal allograft, and more recently, GraftJacket (Wright Medical Technology Inc, Arlington, TN, USA), a human dermal collagen allograft, have been proposed for interposition arthroplasty in young patients with glenohumeral osteoarthritis. METHODS: From 2009 to 2010, GraftJacket was used for glenoid resurfacing combined with humeral resurfacing or a stemmed hemiarthroplasty in 6 patients with a mean age of 47 years (34-57 years). Before GraftJacket was available, 5 patients were treated with a meniscal allograft and 6 with capsular interposition arthroplasty. RESULTS: At a mean of 16 months (9-22 months) after the GraftJacket was implanted, 5 of the 6 patients were revised to a total shoulder arthroplasty or a reverse total shoulder arthroplasty. The sixth patient was dissatisfied but declined further surgery. The mean relative, preoperative Constant score decreased from 35% (range, 13%-61%) to 31% (range, 15%-43%) at revision or latest follow-up. Of the 5 patients with meniscal allograft, 3 underwent revision at a mean of 22 months (range, 12-40 months), and 4 of the 6 patients with capsular interposition were revised at a mean of 34 months (range, 23-45 months). The mean relative Constant scores preoperatively and at revision or latest follow-up were 44% (range, 19%-68%) and 58% (range, 9%-96%) for the meniscal allograft patients and 47% (range, 38%-62%) and 63% (range, 32%-92%) for the capsular interposition cases. CONCLUSION: In our hands, 3 different types of biological resurfacings combined with humeral hemiarthroplasty have an unacceptable early failure rate.