Biomedical subjects

S W O'Driscoll

Publications and source records attributed to S W O'Driscoll.

At least 19 recordsLinked to original sources

PubMed2006

The effect of the orientation of the radial head on the kinematics of the ulnohumeral joint and force transmission through the radiocapitellar joint.

Background. The treatment of radial head fractures that are not amenable to an open reduction and internal fixation, remains to be a difficult issue. A potential problem with prosthetic replacement of the radial head is the shape of current radial head prostheses. The purpose of this study was to determine the effect of the shape of the radial head on kinematics and load transfer of the elbow. Methods. Kinematics of the elbow and radiocapitellar force transmission were measured in 6 fresh frozen upper extremities. The effect of radial head shape was tested by rotating the head 90 degrees , with a custom-made 'native' radial head prosthesis. 3-D spatial orientation of the ulna showed an average difference in ulnohumeral laxity, between the nominal and 90 degrees conditions, of 0.1 degrees throughout the arc of motion with neutral forearm rotation (maximum: 2 degrees ). Findings. We found an average difference in ulnar axial rotation, of 0.1 degrees (maximum: 1.9 degrees ). No differences showed statistical significance. Radiohumeral joint force was measured and maximally showed a 32 times increase of force in the altered shape conditions. Interpretation. Our results show that the kinematics of the elbow was not affected by altering the shape of the radial head, but it did adversely affect the forces in the radiohumeral joint. This could possibly generate degenerative changes in the elbow.

Biomechanical Phenomena↗

PubMed2005

The kinematic importance of radial neck length in radial head replacement.

Comminuted radial head fractures can be treated with a radial head implant. The effects of lengthening (2.5 mm, 5 mm) and shortening (2.5 mm, 5 mm) of the radial neck, were compared to the nominal length in six human upper extremity cadavers. Total varus-valgus laxity and ulnar rotation were recorded. We hypothesized that restoring the exact length of the radius is important to maintain normal kinematics in the elbow joint. Lengthening or shortening of more than 2.5 mm significantly changed elbow kinematics. Lengthening caused a significant decrease (p < 0.001) in varus-valgus laxity, with the ulna tracking in varus and external rotation. Shortening caused a significant increase in varus-valgus laxity (p < 0.001) and ulnar rotation (p < 0.001), with the ulna tracking in valgus and internal rotation. Our study suggests that a restoration of radial length is important and that axial understuffing or overstuffing the radiohumeral joint by 2.5 mm or more, will alter elbow kinematics.

Aged↗

PubMed2005

Intrinsic constraint of unlinked total elbow replacements--the ulnotrochlear joint.

BACKGROUND: Many unlinked total elbow replacement designs with radically differing articular geometries exist, suggesting that there is no consensus regarding an optimal design. A feature inherent to the articular design is the intrinsic constraint afforded to the joint by the implant. Our aim was to compare the intrinsic constraints of unlinked implants with that of the normal ulnotrochlear joint. METHODS: We tested twelve cadaveric ulnotrochlear joints with a custom-made multiple-axis materials testing machine. With compressive loads ranging from 10 to 100 N, the joints were moved in either valgus or varus directions at 90 degrees of flexion. The ulnotrochlear components from a single example of five medium-sized unlinked elbow replacements (Ewald, Kudo, Pritchard ERS, Sorbie-Questor, and Souter-Strathclyde) were also tested. The recorded measurements included the torques and forces, angular displacement, and axial displacement of the humerus relative to the ulna. RESULTS: In general, the peak torque and the constraint ratio significantly increased with increasing compressive load for the implants as well as for the normal elbow. In valgus displacement, the Souter-Strathclyde implant had the highest and the Sorbie-Questor had the smallest peak torque and the Souter-Strathclyde had the highest and the Ewald had the smallest constraint ratio. In varus displacement, the Kudo had the highest and the Ewald had the smallest peak torque and constraint ratio. CONCLUSIONS: The constraint ratio is a characteristic that is useful for describing elbow joint behavior and for comparing the behavior of implants with that of the human elbow. Of the unlinked implants tested, the Souter-Strathclyde and Kudo prostheses most closely approximated the behavior of the human elbow joint. Implants that resemble the human elbow in appearance do not replicate normal behavior consistently, whereas other implants that do not resemble the human elbow closely do not deviate markedly from human behavior. Thus, much basic information about elbow form and function is needed to improve the performance of total elbow prostheses.

Aged↗

PubMed2005

Ligamentous repair and reconstruction for posterolateral rotatory instability of the elbow.

We describe the intermediate results of lateral ligamentous repair or reconstruction for posterolateral rotatory instability of the elbow. Between 1986 and 1999, we performed 12 direct repairs and 33 ligament reconstructions with a tendon autograft. One patient was lost to follow-up and 44 were retrospectively studied at a mean of six years (2 to 15). Surgery restored stability in all except five patients. In two the elbow became stable after a second procedure. The mean post-operative Mayo elbow performance score was 85 points (60 to 100). The result was classified as excellent in 19, good in 13, fair in seven and poor in five patients. Thirty-eight patients (86%) were subjectively satisfied with the outcome of the operation. Better results were obtained in patients with a post-traumatic aetiology (p = 0.03), those with subjective symptoms of instability at presentation (p = 0.006) and those who had an augmented reconstruction using a tendon graft (p = 0.04). Reconstruction using a tendon graft seems to provide better results than ligament repair and the results do not seem to deteriorate with time. The outcome of this procedure is less predictable in patients with no subjective instability.

Adolescent↗

PubMed2004

Anatomical considerations of the radius.

Most radial head prostheses do not seem to be based on anatomic data. This may be due partly to the great variation of radial morphology. More importantly, few articles report on the dimensions of the radius. Authors have mainly studied dimensions of the radial head, with less emphasis to the relationship with the rest of the radius. Dimensions of, and relationship between, the proximal and the rest of the radius were measured on 27 fresh-frozen cadaveric upper extremities. Radial head, articulating surface, diaphysis, and distal radius were measured. Angles between the radial neck and diaphysis were defined and calculated. Axes of the distal and proximal radius were defined and radial torsion was calculated. Repeated measures were done by two observers in ten specimens. Inter- and intra-class correlation coefficients were very acceptable. Radial dimensions were found to be highly variable. Calculation of radial torsion showed the largest range. The average torsion was 54 degrees (range = 23-78 degrees). Radial length was 235 mm (range = 207-269 mm). Radial neck length was 13 mm (range = 9-19 mm). We found an average proximal diaphysis-neck angle of 17 degrees (range = 6-28 degrees). End to end-neck angle was 13 degrees (range = 4-22 degrees). Our findings indicate that even with a perfectly anatomical prosthesis, restoration of the anatomical situation can only be achieved when the implant is placed in the correct position. Instrumentation should be developed to allow accurate and reproducible implantation. The measurements we provide may aid this development.

Aged↗

PubMed2004

The effect of the orientation of the noncircular radial head on elbow kinematics.

OBJECTIVE: The objective of this study was to identify the effect of radial head shape and orientation on elbow kinematics in the otherwise intact elbow. DESIGN: Biomechanical study, analyzing simulated active motion of cadaveric arms. BACKGROUND: A discrepancy exists between the noncircular anatomy of the radial head and radial head prostheses. The effect of radial head shape is unknown. METHODS: Kinematic effects of radial head shape were tested in six fresh-frozen upper extremities. A custom-made native radial head prosthesis was used to simulate altered shape conditions, by rotating the radial head 90 degrees. Three-dimensional spatial orientation of the ulna was recorded, during simulated active motion. A three factor ANOVA was used to compare (a) nominal and 90 degrees oriented conditions, (b) throughout the flexion arc (c) in three forearm positions (P < 0.05). Post-hoc Tukey tests were done to assess significance. RESULTS: No significant effect of altering radial head shape was found on total ulnohumeral laxity and angulation during gravity valgus stress. We did find a significant effect on total ulnar axial rotation and rotation during gravity valgus stress. CONCLUSION: The outer shape of the radial head seems to change rotation of the ulna during flexion-extension in an otherwise intact elbow. RELEVANCE: The shape of the radial head effects intact elbow kinematics. Clinical importance of this finding is clear. If a sub-optimally placed radial head prosthesis were to be used in an otherwise intact elbow, the elbow could be at risk for early ulnohumeral arthritis.

Biomechanical Phenomena↗

PubMed2004

Animal models for cartilage reconstruction.

Animal models are widely used to develop and evaluate tissue-engineering techniques for the reconstruction of damaged human articular cartilage. For the purpose of this review, these model systems will include in vitro culture of animal cells and explants, heterotopic models of chondrogenesis, and articular cartilage defect models. The objectives for these preclinical studies are to engineer articular cartilage for the functional restoration of a joint surface that appears anatomically, histologically, biologically, biochemically, and mechanically to resemble the original joint surface. While no animal model permits direct application to humans, each is capable of yielding principles on which decisions can be made that might eventually translate into a human application. Clearly, the use of animal models has and will continue to play a significant role in the advancement of this field. Each animal model has specific advantages and disadvantages. The key issue in the selection of an appropriate animal model is to match the model to the question being investigated and the hypothesis to be tested. The purpose of this review is to discuss issues regarding animal model selection, the benefits and limitations of these model systems, scaffold selection with emphasis on polymers, and evaluation of the tissue-engineered articular cartilage.

Animals↗

PubMed2004

Detrimental effects of overstuffing or understuffing with a radial head replacement in the medial collateral-ligament deficient elbow.

BACKGROUND: Comminuted radial head fractures associated with an injury of the medial collateral ligament can be treated with a radial head implant. We hypothesized that lengthening and shortening of the radial neck would alter the kinematics and the pressure through the radiocapitellar joint in the medial collateral ligament-deficient elbow. METHODS: The effects of lengthening (2.5 and 5 mm) and shortening (2.5 and 5 mm) of the radial neck were assessed in six human cadaveric upper extremities in which the medial collateral ligament had been surgically released. The three-dimensional spatial orientation of the ulna was recorded during simulated active motion from extension to flexion. Total varus-valgus laxity and ulnar rotation were measured. Radiocapitellar joint pressure was assessed with use of pressure-sensitive film. RESULTS: Radial neck lengthening or shortening of >/=2.5 mm significantly changed the kinematics in the medial collateral ligament-deficient elbow. Lengthening caused a significant decrease (p < 0.05) in varus-valgus laxity and ulnar rotation (p < 0.05), with the ulna tracking in varus and external rotation. Shortening caused a significant increase in varus-valgus laxity (p < 0.05) and ulnar rotation (p < 0.05), with the ulna tracking in valgus and internal rotation. The pressure on the radiocapitellar joint was significantly increased after 2.5 mm of lengthening. CONCLUSIONS: This study suggests that accurate restoration of radial length is important and that axial understuffing or overstuffing of the radiohumeral joint by >/=2.5 mm alters both elbow kinematics and radiocapitellar pressure. CLINICAL RELEVANCE: This in vitro cadaver study indicates that a radial head replacement should be performed with the same level of concern for accuracy and reproducibility of component position and orientation as is appropriate with any other prosthesis.

Aged↗

PubMed2003

Gliding properties of the long head of the biceps brachii.

To elucidate the role of mechanical forces that resist motion of the long head of the biceps brachii, the gliding resistance of the tendon during abduction and adduction was measured. Nine human cadaveric glenohumeral joints were obtained (mean age 68 years, range 47-84). A testing device was developed to simulate glenohumeral abduction and adduction motion. Gliding resistance was calculated as the force differential on the proximal and distal ends of the biceps brachii at five glenohumeral angles (15 degrees, 30 degrees, 45 degrees, 60 degrees and 75 degrees ). The average gliding resistance in abduction at 15 degrees, 30 degrees, 45 degrees, 60 degrees and 75 degrees for a 4.9 N load was 0.41, 0.40, 0.36, 0.32 and 0.28 N, respectively. At these same angles, but during adduction motion, the force on the proximal tendon end was either identical or less than the distal tendon end (p>0.46) indicating a lack of resistance and even a phenomena of "negative" resistance in which some other force overcame the friction. The difference in gliding resistance between abduction and adduction was significant (p<0.05). The results indicate that forces opposing biceps tendon gliding are more complicated than simply due to friction. Tendon deformation inside the bicipital groove produces a direction-dependent effect due to a mechanism of elastic recoil. Understanding forces that are absorbed by the tendon during active motion may provide insight into pathological changes that develop inside and around the tendon.

Friction↗

PubMed2003

Combined effects of insulin-like growth factor-1 and transforming growth factor-beta1 on periosteal mesenchymal cells during chondrogenesis in vitro.

OBJECTIVE: Periosteum contains undifferentiated mesenchymal stem cells that have both chondrogenic and osteogenic potential, and has been used to repair articular cartilage defects. During this process, the role of growth factors that stimulate the periosteal mesenchymal cells toward chondrogenesis to regenerate articular cartilage and maintain its phenotype is not yet fully understood. In this study, we examined the effects of insulin-like growth factor-1 (IGF-1) and transforming growth factor-beta1 (TGF-beta1), alone and in combination, on periosteal chondrogenesis using an in vitro organ culture model. METHODS: Periosteal explants from the medial proximal tibia of 2-month-old rabbits were cultured in agarose under serum free conditions for up to 6 weeks. After culture the explants were weighed, assayed for cartilage production via Safranin O staining and histomorphometry, assessed for proliferation via proliferative cell nuclear antigen (PCNA) immunostaining, and assessed for type II collagen mRNA expression via in situ hybridization. RESULTS: IGF-1 significantly increased chondrogenesis in a dose-dependent manner when administered continuously throughout the culture period. Continuous IGF-1, in combination with TGF-beta1 for the first 2 days, further enhanced overall total cartilage growth. Immunohistochemistry for PCNA revealed that combining IGF-1 with TGF-beta1 gave the strongest proliferative stimulus early during chondrogenesis. In situ hybridization for type II collagen showed that continuous IGF-1 maintained type II collagen mRNA expression throughout the cambium layer from 2 to 6 weeks. CONCLUSION: The results of this study demonstrate that IGF-1 and TGF-beta1 can act in combination to regulate proliferation and differentiation of periosteal mesenchymal cells during chondrogenesis.

Animals↗

PubMed2003

Partial posteromedial olecranon resection: a kinematic study.

BACKGROUND: The posteromedial aspect of the olecranon process is a site of impingement and subsequent osteophyte development in throwing athletes. Treatment with débridement, with resection of osteophytes and varying amounts of normal olecranon bone, is common. We found no reports in the literature concerning the effects of resecting different amounts of normal bone from the posteromedial aspect of the olecranon. We hypothesized that excessive resection would increasingly alter elbow kinematics and that an optimum amount of olecranon resection could be identified. METHODS: We investigated the kinematic effects of increasing valgus and varus torques and posteromedial olecranon resections, in twelve cadaveric elbows, with use of an electromagnetic tracking device. Two valgus and two varus torques were applied, and three sequential resections were performed in 3-mm steps from 0 mm to 9 mm. Statistical analyses included paired t tests, 95% confidence intervals, a one-factor analysis of variance with repeated measures, and a post hoc test when significance was established. RESULTS: Sequential partial resection of the posteromedial aspect of the olecranon resulted in stepwise increases in valgus angulation with valgus torque. Clear differences were seen at each level of resection. A pattern of increased valgus angulation also was seen in association with increased valgus torque. Increased valgus torque resulted in a trend toward increased axial internal rotation of the ulna, whereas increased osseous resection resulted in a decrease in the absolute degree of internal rotation or, in some specimens, increased external rotation. CONCLUSIONS: Although no single critical amount of olecranon resection was identified, valgus angulation of the elbow increased in association with all resections, with a marked increase occurring in association with a 9-mm resection. Our findings challenge the rationale of removing any amount of normal olecranon bone in throwing athletes as doing so may increase strain on the medial collateral ligament. The implications for the professional throwing athlete are important, and we recommend that bone removal from the olecranon be limited to osteophytes, without the removal of normal bone.

Aged↗

PubMed2002

Expression of beta1 integrins during periosteal chondrogenesis.

OBJECTIVE: The interactions between integrins and extracellular matrix proteins are known to modulate cell behavior, and may be involved in regulating cartilage formation and repair. The purpose of this study was to determine the patterns and localization of expression of the beta1 integrins during cartilage formation by periosteum, which is used to repair articular cartilage. DESIGN: Periosteal explants from 2-month-old rabbit medial proximal tibiae were cultured in agarose suspension for 0 to 6 weeks, with 10 ng/ml transforming growth factor-beta1 added for the first 2 days of culture. Integrin expressions were measured by reverse transcriptase-polymerase chain reaction (RT-PCR) and localized by immunohistochemistry. RESULTS: Normal periosteum expressed the alpha1, alpha3, alpha5, beta1 subunits at low levels, and the proteins for all but the alpha3 subunits were identified by immunohistochemistry in the periosteum. Significant two- to five-fold up-regulation of the mRNA expression of the alpha1, alpha3, alpha5 and beta1 integrin subunits during the early proliferative stage of chondrogenesis was observed. The initial change was a five-fold increase in alpha5 expression on day 2 and a two-fold increase in alpha3 expression. On day 5, alpha1 expression was up-regulated (four-fold). beta1 expression was broadly up-regulated (three to four-fold) from day 5 to 14. In the early stage of chondrocyte differentiation, after day 14, alpha1 expression was down-regulated, while there was upregulation of alpha3 (three-fold), alpha5 (three-fold) and beta1 (four-fold) expressions. Thereafter, alpha1 expression was down-regulated, while alpha3, alpha5 and beta1 expressions were up-regulated again during matrix synthesis. Immunohistochemistry confirmed this late decrease in alpha1 levels and increase in alpha3, alpha5 and beta1 levels in chondrocytes. CONCLUSIONS: These observations indicate that the beta1 integrins play an important role in the process of chondrogenesis in periosteum.

Animals↗

PubMed2002

Effect of pregnancy on joint contracture in the rat knee.

As there is evidence that ligamentous laxity is affected by the female hormones, we hypothesized that hormonal changes occurring during pregnancy could have a therapeutic role in preventing the development of a joint contracture. Knee joint contractures were created in pregnant and nonpregnant rats. After 2 wk of immobilization, the degree of contracture was measured with structural properties of the medial collateral and anterior cruciate ligaments and the pubic symphysis. Although not statistically significant, there was a general trend toward reduced contracture in pregnant compared with nonpregnant rats. Cutting the posterior capsule significantly decreased contracture for both the pregnant and nonpregnant groups, confirming the contribution of capsular structures to contracture. Ultimate loads of the medial collateral and anterior cruciate ligaments significantly decreased after immobilization compared with control, but there was no significant effect due to pregnancy. Stiffness and ultimate load of the pubic symphysis were not significantly different between pregnant and nonpregnant groups. The trend toward reduced contracture with pregnancy points toward a possible therapeutic role for female hormones in the prevention of postoperative and/or posttraumatic joint contracture.

Animals↗

PubMed2002

Synovial osteochondromatosis of the elbow.

We present 12 patients with synovial osteochondromatosis of the elbow treated by synovectomy. Histological review showed that seven cases were primary and five secondary osteochondromatosis. The patients with primary disease had a mean improvement in the flexion arc from a preoperative value of 40 degrees to 123 degrees to 5 degrees to 128 degrees when reviewed at a mean of nine years after operation. The secondary group had a mean improvement in the flexion arc from a preoperative value of 21 degrees to 98 degrees to 4 degrees to 131 degrees at a mean of 6.8 years after operation. There was recurrence in two of seven patients in the primary group and three of five in the secondary group. Osteoarthritis developed in six elbows in the primary and in three in the secondary group. Osteoarthritis secondary to synovial osteochondromatosis is progressive. In the established condition, the distinction between primary and secondary disease may be of greater histological than clinical relevance.

Adolescent↗

PubMed2002

Biomechanical comparison of effects of supraspinatus tendon detachments, tendon defects, and muscle retractions.

BACKGROUND: Rotator cuff ruptures are frequently associated with loss of strength of the shoulder. However, the characteristics of the rotator cuff tear that are responsible for the loss of force generation and transmission have not yet been identified. The purpose of this study was to compare the effects of supraspinatus tendon detachments, tendon defects, and muscle retractions on in vitro force transmission by the rotator cuff to the humerus. METHODS: The rotator cuff tendons from ten cadaver shoulders were loaded proportionally to the respective cross-sectional areas of their muscles. A fiberglass rod was cemented into the medullary canal of the humerus and connected to a three-component load cell for the measurement of the forces transmitted by the rotator cuff to the humerus. This study was performed with the humerus in a hanging arm position and with various sizes of supraspinatus tendon detachments, tendon defects, and muscle retractions. RESULTS: Detachment or creation of a defect involving one-third or two-thirds of the supraspinatus tendon resulted in a minor reduction in the force transmitted by the rotator cuff (< or =5%), while detachment or creation of a defect involving the whole tendon resulted in a moderate reduction (11% and 17%, respectively). Simulated muscle retraction involving one-third, two-thirds, and the whole tendon resulted in losses of torque measuring 19%, 36%, and 58%, respectively. Side-to-side repair of the one-third and two-thirds defects nearly restored the force transmission capability, whereas a deficit remained after side-to-side repair following complete resection. CONCLUSIONS: Our results support the rotator cable concept and correspond to the clinical observation that patients with a small rupture of the rotator cuff may present without a loss of shoulder strength. Muscle retraction is potentially an important factor responsible for loss of shoulder strength following large rotator cuff ruptures. CLINICAL RELEVANCE: Supraspinatus muscle retraction diminishes glenohumeral abduction torque significantly more than either a defect in the tendon or a simple detachment of the tendon from the tuberosity. In cases of irreparable defects, side-to-side repair may be worthwhile to restore muscle tension and the integrity of the rotator cable.

Biomechanical Phenomena↗

PubMed2001

Treatment of instability after total elbow arthroplasty.

Instability after total elbow arthroplasty can be due to incorrect component selection or position, inadequacy of the medial or lateral ligaments or triceps tendon, polyethylene wear, limb malalignment, or trauma. Patients with significant loss of bone structure, ligament deficiency, and tendon deficiency around the elbow are at increased risk of instability following total elbow arthroplasty.

Arthroplasty, Replacement↗

PubMed2001

Dynamic inferior stabilizers of the shoulder joint.

BACKGROUND: The glenohumeral joint is soft-tissue balanced. However, few studies have focused on its dynamic inferior stabilizers. OBJECTIVE: The objective of this study was to investigate the dynamic contributions of five shoulder muscles to inferior stability of the glenohumeral articulation in four joint positions. METHODS: The anterior, lateral and posterior deltoid, supraspinatus, short head of biceps, coracobrachialis and long head of triceps from ten cadaveric shoulders were tested in 0 degrees, 30 degrees, 60 degrees and 90 degrees of glenohumeral abduction. A constant inferior force of 15 N was applied to the humerus. The tendons were loaded sequentially in proportion to their respective muscle's cross-sectional area. Translations of the humeral head on the glenoid were recorded with a 3-Space tracking device. RESULTS: The lateral deltoid (8.2 mm, SD 4.8 mm) was potentially most effective in superior translation of the humeral head followed by the posterior deltoid (7.7 mm, SD 4.8 mm). The coracobrachialis and short head of biceps had considerable capability to translate the humeral head superiorly (2.8 mm, SD 1.3 mm) while the supraspinatus showed the weakest effects (1.3 mm, SD 0.5 mm). RELEVANCE: Strengthening exercises of the deltoid may be useful in the treatment of inferior glenohumeral instability, while the supraspinatus seems to be less important for inferior glenohumeral stability than previously assumed.

Biomechanical Phenomena↗

PubMed2001

The effect of forearm rotation on laxity and stability of the elbow.

OBJECTIVE: The purpose of this study was to quantify the relationship between forearm rotation and valgus/varus laxity of the elbow joint over the range of elbow flexion. BACKGROUND: There is little known about the influence of forearm rotation on the laxity and stability of the elbow joint. The general opinion exists that forearm rotation does not significantly influence the laxity and stability of the elbow joint. METHODS: Nine fresh-frozen cadaver elbows were used. Passive elbow flexion with the forearm in neutral rotation and in 40 degrees and 80 degrees of pronation and supination was performed under valgus/varus loads: (1) in intact elbows; (2) after a lateral surgical approach (lateral epicondylar osteotomy of the distal humerus); (3) after release of the anterior bundle of the medial collateral ligament; and (4) after release of the anterior bundle of the medial collateral ligament plus radial head resection. Valgus/varus elbow laxity was quantified using an electromagnetic tracking device. RESULTS: There was a statistically significant effect (P < 0.05) of forearm rotation on valgus/varus laxity throughout the range of flexion. The laxity was always greater in pronation than in supination, regardless of the surgical approach or the integrity of the anterior bundle of the medial collateral ligament or radial head. CONCLUSIONS: Valgus/varus laxity of the elbow is forearm rotation-dependent. The potential role of this effect should be considered and controlled for in the design of studies examining laxity and stability of the elbow joint. RELEVANCE: The observation that forearm pronation increases valgus/varus laxity, particularly in medial collateral ligament deficient elbows, implies a possible additional factor in throwing kinematics that might put professional baseball pitchers at risk of medial collateral ligament injury due to chronic valgus overload. Our data indicate that forearm rotation should be considered during the clinical examination of elbow instability.

Aged↗