Mark K. Bowen

In vivo human knee joint dynamic properties as functions of muscle contraction and joint position

Information on the dynamic properties (joint stiffness, viscosity and limb inertia) of the human knee joint is scarce in the literature, especially for actively contracting knee musculature. A joint driving device was developed to apply small-amplitude random perturbations to the human knee at several flexion angles with the subject maintaining various levels of muscle contraction. It was found that joint stiffness and viscosity increased with muscle contraction substantially, while limb inertia was constant. Stiffness produced by the quadriceps was highest at 30 degrees flexion and decreased with increasing or decreasing flexion angle, while knee flexors produced highest stiffness at 90 degree flexion. When knee flexion was < 60 degrees, stiffness produced by the quadriceps was higher than that of the hamstrings and gastrocnemius at the same level of background muscle torque, while knee flexor muscles produced higher stiffnesses than the quadriceps at 90 degree flexion. Similar but less obvious trends were observed for joint viscosity. Passive joint stiffness at full knee extension was significantly higher than in more flexed positions. Surprisingly, as the knee joint musculature changed from relaxed to contracting at 50% MVC, system damping ratio remained at about 0.2. This outcome potentially simplifies neuromuscular control of the knee joint. In contrast, the natural undamped frequency increased more than twofold, potentially making the knee joint respond more quickly to the central nervous system commands. The approach described here provides us with a potentially valuable tool to quantify in vivo dynamic properties of normal and pathological human knee joints.

Acromioclavicular Joint Injuries and Distal Clavicle Fractures

&NA; The acromioclavicular joint is commonly affected by traumatic and degenerative conditions. Most injuries are due to direct trauma, such as a fall on the shoulder. Six types of acromioclavicular sprains and three types of distal clavicle fractures have been described in adults. Although there is general agreement on treatment of type I, II, IV, V, and VI acromioclavicular injuries, the treatment of type III injuries remains controversial. Studies have shown no distinct advantage for surgical reconstruction over nonoperative treatment. Because type II distal clavicle fractures are prone to nonunion, operative fixation may be advisable to avoid this complication.

Suprascapular Nerve Entrapment at the Spinoglenoid Notch in a Professional Baseball Pitcher

Suprascapular nerve injuries at the spinoglenoid notch are uncommon. The true incidence of this lesion is unknown; however, it appears to be more common in athletes who participate in sports involving overhead activities. When a patient is being evaluated for posterior shoulder pain and infraspinatus muscle weakness, electrodiagnostic studies are an essential part of the evaluation. Electromyography will identify an injury to the suprascapular nerve as well as assist in localizing the site of injury. In addition, imaging studies are also indicated to help exclude other diagnoses that can mimic a suprascapular nerve injury. The initial management should consist of cessation of the aggravating activity along with an organized shoulder rehabilitation program. If the patient fails to improve with 6 months to 1 year of nonoperative management, surgical exploration of the suprascapular nerve should be considered. Release of the spinoglenoid ligament with resultant suprascapular nerve decompression may result in relief of pain and a return of normal shoulder function.

Biomechanical and histological evaluation of osteochondral transplantation in a rabbit model.

Background Biomechanical and histological properties of osteochondral transplantation have not been extensively examined. Hypothesis Osteochondral grafts have properties similar to native articular cartilage. Study Design Controlled laboratory study. Methods A 2.7 mm (diameter) × 4.0 mm (depth) osteochondral defect was created in 17 New Zealand white rabbit knees. An osteochondral graft, harvested from the contralateral knee, was transplanted into the defect. Eight rabbits were sacrificed each at 6 and 8 weeks. Results The 12-week grafts (1213.6 ± 309.0 N/mm) had significantly higher stiffness than the 6-week grafts (483.1 ± 229.1 N/mm; P< .001) and of normal cartilage (774.8 ± 117.1 N/mm; P< .003). Stiffness of the 6-week grafts was significantly lower than normal cartilage (P< .036). At all time points, full-thickness defects had significantly lower stiffness than normal cartilage (P< .001). Histologically, transplanted grafts scored significantly higher than the full-thickness defects (P< .001). The defects showed inconsistent, fibrocartilage healing. The grafts demonstrated cartilage viability, yet with a persistent cleft between the graft and host. Conclusions Osteochondral transplants undergo increased stiffness in the short term, with evidence of structurally intact grafts. Clinical Relevance Osteochondral transplantation may be a viable treatment option; however, long-term investigation on graft function is necessary.

Anatomy and histological characteristics of the spinoglenoid ligament

The spinoglenoid (inferior transverse scapular) ligament, when present, is located at the spinoglenoid notch. The ligament originates on the spine of the scapula and inserts on the superior margin of the glenoid neck. Because of discrepancies in the literature, we sought to determine its prevalence and to define its histological characteristics. We dissected 112 shoulders of seventy-six cadavera and classified the ligament as absent or an insubstantial structure, a thin fibrous band (type I), or a distinct ligament (type II). We found no distinct ligamentous structure in twenty-two shoulders (20 percent), a type-I ligament in sixty-eight shoulders (20 percent), a type-I ligament in sixty-eight shoulders (61 percent), and a type-II ligament in twenty-two shoulders (20 percent). Overall, ninety (80 percent) of the shoulders had a fibrous band of tissue that, together with the spine of the scapula, formed a narrow fibro-osseous tunnel through which the suprascapular nerve traveled. The bone-spinoglenoid ligament-bone complexes from three specimens were analyzed histologically. There were two type-I ligaments and one type-II ligament; all three ligaments were composed of collagen fibers. One type-I ligament and the type-II ligament demonstrated Sharpey fibers at their origin on the spine of the scapula. The other type-I ligament attached to the spine of the scapula through the periosteum. All three ligaments inserted into the periosteum of the glenoid neck. CLINICAL RELEVANCE: The spinoglenoid ligament may be clinically relevant in two respects. First, the ligament may limit mobilization and advancement of the infraspinatus tendon during repair of a massive tear of the rotator cuff, placing the distal part of the suprascapular nerve at risk. Second, the spinoglenoid ligament represents a potential site for nerve entrapment, particularly with the added stress of traction that can occur with overhead athletic activities.

Arthroscopic treatment of acromioclavicular joint injuries and results

Injuries and conditions that affect the AC joint are common. Low-grade separations, degenerative conditions, and osteolysis of the distal clavicle are frequently dealt with by the treating physician. Proper assessment requires a thorough history, examination, and radiologic work-up. An injection of bupivicaine into the AC joint can be a very useful test to evaluate the source of pain about the symptomatic shoulder. Most conditions affecting the AC joint can be treated conservatively, but patients who do not respond to these treatments or athletes who do not wish to modify their activities may require resection of the distal clavicle and the AC joint. Operative intervention can be performed as an open procedure with good results. Recent advances in operative arthroscopic procedures allow us to replicate and exceed the results of the open resection. Arthroscopic resection can be undertaken via a direct approach that does not violate the subacromial space or via an indirect or bursal approach. The indirect approach allows you to assess both the subacromial space and the AC joint because impingement pathology and subacromial compromise are frequently associated with AC change. The advantage of an arthroscopic resection is its ability to be performed as an outpatient procedure with less compromise of musculotendinous structures, shorter rehabilitation, and quicker return to activity. The amount of bone resection necessary is less than with the open procedure because of the ability to preserve the stabilizing properties of the superior AC ligaments. Resection of 4 mm to 8 mm of bone is all that may be required to give uniformly good results. Arthroscopic resection of the distal clavicle is technically demanding and requires skill and familiarity with other arthroscopic shoulder procedures. Complications related to this procedure are relatively infrequent and include infection, residual pain, lack of adequate bone resection, and instability, particularly in patients with previous grade 1 and 2 separations. Less commonly noted is the symptomatic development of heterotopic bone. To the accomplished arthroscopic shoulder surgeon, arthroscopic resection of the symptomatic AC joint gives excellent clinical results that allow a compromised athlete a relatively quick return to desired sport activities.

Coverage of the Anterior Cruciate Ligament Femoral Footprint Using 3 Different Approaches in Single-Bundle Reconstruction A Cadaveric Study Analyzed by 3-Dimensional Computed Tomography

Background: Performing a single-bundle anterior cruciate ligament (ACL) reconstruction within the femoral footprint is important to obtain a functional graft and a stable knee. Hypothesis: There will be a significant difference in the ability of 3 ACL reconstruction techniques to reach and cover the native femoral footprint. Study Design: Controlled laboratory study. Methods: The percentage of the ACL footprint covered by the femoral tunnel was compared after 3 different techniques to target the footprint: transtibial (TT), inside-out/anteromedial (IO), and outside-in/transfemoral (OI). Fourteen cadaveric knee specimens with a mean age of 67.5 years were used. For each knee, the TT technique utilized a 7.5-mm offset guide, the IO technique was performed through an accessory anteromedial portal, and the OI technique was carried out through the femur from the external wall of the lateral condyle. Entry points in the footprint were spotted with markers, and orientations (sagittal and frontal) of each drill guide were noted. The distal femurs were sawed and scanned, and 3-dimensional image reconstructions were analyzed. The virtual drilled area (reamer diameter, 8 mm) depending on the entry point and the sagittal/frontal orientation of the drill guide was calculated and reported for each of the 3 techniques. The distance from the tunnel center to the ACL center, percentage of the femoral tunnel within the ACL footprint, and percentage of the ACL footprint covered by the tunnel were calculated and statistically compared (analysis of variance and t test). Results: The average distance to the native femoral footprint center was 6.8 ± 2.68 mm for the TT, 2.84 ± 1.26 mm for the IO, and 2.56 ± 1.39 mm for the OI techniques. Average percentages of the femoral tunnel within the ACL footprint were 32%, 76%, and 78%, and average percentages of the ACL footprint covered by the tunnel were 35%, 54%, and 47%, for the TT, IO, and OI techniques, respectively. No significant difference was observed between the IO and OI techniques (P = .11). The TT approach gave less satisfactory coverage on all testing criteria. Conclusion: The IO and OI techniques allowed for creation of a tunnel closest to the ACL femoral footprint center. Despite this fact and even if the average percentage of the drilled area included in the femoral footprint was close to 80% for these 2 techniques, the average percentage of the ACL footprint covered by the tunnels was <55% for all 3 techniques. Coverage of the ACL footprint depended on the entry point, orientation, and diameter of the drilling but also on the size of the footprint. Clinical Relevance: To improve the coverage of the native femoral footprint with a single-bundle graft, in addition to the entry point it may also be necessary to consider the orientation of the drilling to increase the dimensions of the area while respecting the anatomic constraints of the femoral bone and graft geometry.

Efficacy and Safety of Hylan G-F 20 for Symptomatic Glenohumeral Osteoarthritis: A Prospective, Pilot Study

To determine the safety and efficacy of 2 intra‐articular, fluoroscopically guided hylan G‐F 20 injections for painful glenohumeral osteoarthritis.

Multiaxis muscle strength in ACL deficient and reconstructed knees: compensatory mechanism.

PURPOSE It is unclear how muscle strength in tibial rotation and knee abduction change following anterior cruciate ligament (ACL) injury and reconstruction. Such strength changes are likely, considering the oblique orientation of the ACL and the constraint provided by the ACL at various tibial rotation and adduction positions. The purposes of this study were to evaluate multiaxis muscle strength in ACL deficient and reconstructed knees and to gain insights into potential compensatory mechanisms adopted by the patients. METHODS Muscle strength in tibial internal-external rotation, abduction-adduction, and flexion-extension were investigated in 19 chronic ACL deficient, 18 acute ACL deficient, 21 ACL reconstructed, and 23 normal subjects. The strength ratios of flexion/extension, abduction/adduction, and internal/external rotation were determined for each subject and compared across the different populations. RESULTS The chronic ACL deficient patients showed significantly lower strength ratio in internal/external rotation than that of the normal controls and acute ACL deficient subjects (P = 0.02), indicating a compensatory mechanism developed by the patients to unload the ACL and/or to avoid unstable knee positions. For ACL reconstructed patients, the internal/external rotation strength ratio became closer to their counterparts in normal controls than that of chronic ACL deficient patients, presumably reflecting the reduced need for compensation after reconstruction. Furthermore, compared with strength reduction in knee extension, reductions in tibial rotation and abduction strength following ACL reconstruction were less severe and more easy to recover. CONCLUSION A better understanding of changes in multiaxis muscle strength and the associated compensatory mechanism will help us evaluate treatment outcome more accurately and develop more effective treatment modalities with focus on muscles that help protect and unload the ACL.

Case Report Spur Reformation After Arthroscopic Acromioplasty

Rotator cuff pathology has been associated with a hooked acromial morphology. Impingement syndrome has traditionally been considered to be the result of bony encroachment into the subacromial space. This report of a spur recurrence after acromioplasty presents evidence that acromial morphology may be a reactive change attributable to primary rotator cuff insufficiency.