Morphological Measurements of the Proximal Interphalangeal Joint

Novel implant design of the proximal interphalangeal joint using an optimized rolling contact joint mechanism

Background

The aims of this study were to propose a novel implant design for the proximal interphalangeal joint (PIPJ) of the hand using a rolling contact joint (RCJ) mechanism and to derive an optimal implant design based on human PIPJ kinematics.

Methods

In total, 10 participants with normal PIPJs were enrolled in this study. True lateral finger radiographs were obtained in 10° increments from 0º (full extension) to 120° flexion of PIPJ. Radiographs were used to determine the average center of rotation, which formed the basis of a mathematical expression of the PIPJ kinematics. The variations in extensor tendon excursions in relation to the range of motion of PIPJ were determined using results from previous cadaveric studies. As the next step, a PIPJ implant design using an RCJ mechanism that was most consistent with the mathematically expressed PIPJ kinematics and tendon excursions was determined using a constrained optimization algorithm.

Results

The final proposed PIPJ implant had a relatively constant center of rotation over the entire PIPJ range of motion among the participants. In addition, the extensor tendon excursions of the proposed implant as applied to the phalangeal bones were similar to those of the human tendon. The proposed PIPJ implant achieved an acceptable position of the RCJ surface on the proximal and middle phalanges, which was derived from the constrained optimization algorithm.

Conclusions

A novel PIPJ implant design using an RCJ mechanism demonstrated acceptable outcomes in terms of PIPJ human kinematics and tendon excursions.

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.

Change in the collateral and accessory collateral ligament lengths of the proximal interphalangeal joint using cadaveric model three-dimensional laser scanning

The purpose of this study was to assess the lengths of the index and middle finger proximal interphalangeal joint ligaments and determine the relative changes in the collateral and accessory collateral ligament lengths at 0°, 45° and 90° flexion. We generated three-dimensional scans of 16 finger (eight index and eight middle) proximal interphalangeal joints to assess relative changes in ligament length. Significant changes were found between 45°-90° and 0°-90° for the ulnar collateral ligament of the index finger and both collateral ligaments of the middle finger between 45°-90° and 0°-90°. No significant changes in length were found for the radial collateral ligament of the index finger or the accessory collateral ligaments of the index and middle fingers. Overall, it was found that the collateral ligament length changed significantly, but there was no significant change in the accessory collateral ligaments.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

In vitro kinematics of the proximal interphalangeal joint in the finger after progressive disruption of the main supporting structures

BACKGROUND

Fractures and dislocations of the proximal interphalangeal (PIP) joint of the fingers are among the most common causes of injury in the hand. Objective assessment of the kinematic alterations occurring when the supporting structures are disrupted is critical to obtain a more accurate indication of joint stability.

METHODS

An in vitro cadaver model of the hand was used to evaluate the kinematics of the PIP joint in the finger during active unrestrained flexion and extension. The kinematics of the PIP joint following progressive disruption of the main supporting structures was measured using an optical tracking system and compared with those in the intact joint.

RESULTS

Flexion of the intact PIP joint was associated with joint compression, volar displacement, and rotational movements. Release of the main soft-tissue stabilizers and 30 % of volar lip disruption resulted in substantial alteration of several kinematic variables. The normalized maximum dorsal/volar translation was 0.1 ± 1.3 % in the intact group and 14.4 ± 11.3 % in the injured joint.

CONCLUSIONS

In the intact PIP joint, rotations and translation are strongly coupled to the amount of joint flexion. Gross instability of the PIP joint occurs when disruption of the collateral ligaments and volar plate is accompanied by resection of at least 30 % of volar lip of the middle phalanx. Collateral ligament injuries, volar plate injuries alone, and fractures at the volar base of the middle phalanx that involve less than 30 % of the articular surface are unlikely to result in gross instability and may be managed effectively with non-operative treatments.

Curvatures of the DIP joints of the hand

BACKGROUND

The distal interphalangeal (DIP) joints of the hand are highly susceptible to osteoarthritis and trauma. Surgical treatment options mandate accurate characterization of their osseous anatomy; however, there are few studies that describe this. We describe the curvatures of the DIP joints by measuring the bone morphology using advanced imaging and modeling methods.

METHODS

The fingers of 16 right hand fresh frozen human cadavers were analyzed. Fingers showing signs of DIP joint arthritis were excluded. The fingers were scanned using microtomography (microCT). Measurements of the bony morphology were made using models created from the scans.

RESULTS

In each finger, there is no statistically significant difference between the radii of curvature of the ulnar and radial condyles of the middle phalanx head. Conversely, the radius of curvature of the distal phalanx ulnar groove is significantly greater than that of the radial groove. The radii of curvature of the groove of the distal phalanx and the condyles of the middle phalanx displayed nonconformity with disparity increasing from the index to small fingers. Remarkably, the radius of curvature of the distal phalanx central ridge and the mean radius of the middle phalanx condyles are essentially the same.

CONCLUSION

The purpose of this study is to gain better insight into the DIP joints of the hand. The asymmetry between the distal phalanx grooves and the middle phalanx condyles suggests that there may be a translational component to DIP joint motion. Our understanding of morphology may lend insight into the biomechanics and disease progression within the DIP joints.

Estimation of base of middle phalanx size using anatomical landmarks

PURPOSE

To determine whether there is a measurable and reproducible relationship between the articular surface size of the middle phalanx base and the size of the middle phalanx head and proximal phalanx length of the same finger.

METHODS

Size of the articular surface of the middle phalanx base, size of the middle phalanx head, and proximal phalanx length were measured in 84 lateral radiographs by 3 observers.

RESULTS

The ratio of articular surface size of the middle phalanx base to the proximal phalanx length of the same finger was 0.17. The ratio of articular surface size of the middle phalanx base to the size of the middle phalanx head of the same finger was 1.34. The intraclass correlation (ICC) among 3 raters was 0.99 for proximal phalanx length and 0.88 for size of the middle phalanx head.

CONCLUSIONS

Knowledge of this relationship and ratios allow for accurate estimation of the percentage of articular surface involvement in a fracture of the middle phalanx base. The ICC was highest for measuring proximal phalanx length, making it the most reliable measurement for estimation of the articular surface size.

CLINICAL RELEVANCE

This quantitative estimate may be useful for clinical research and is applicable to patient care.

Effects of substituting anthropometric joints with revolute joints in humanoid robots and robotic hands: a case study

In the human body there are many joints whose functions are very similar to revolute joints. To avoid the complexity of these joints, they are usually substituted by revolute joints in many humanoid robots. Revolute joints have purely rotational motion along their fixed axis, while real joints in the human body have Instantaneous Rotational Axis (IRA) due to their configuration. Substitution of this kind of human joints with revolute (hinge) joints in robots changes the kinematics of joints. Knowing the exact characteristics of the moving axis of rotation in human joints is a prerequisite for the kinematic study of a joint. Here the main geometrical difference between these kinds of joints in humans and their simplified (hinge-like) models in robots is described. Then, as a case study, the mechanism of the three joints of the index finger are compared with their hinge-like model using a multi-body code to understand when revolute joints can be substituted for anthropometric joints in hand exoskeletons and robotic hands. Furthermore, the position of IRA and its distance from the center of the condyle of the joint are presented. The concept and the results can be extended for other fingers and all similar joints, and can be used in humanoid robots, hand exoskeletons and robotic hands.

Structural comparison of the finger proximal interphalangeal joint surfaces and those of the third toe: suitability for joint reconstruction

PURPOSE

This study compared the degree of surface structural similarity between finger proximal interphalangeal joints and third toe articular surfaces to assess the appropriateness of using partial toe articular osteochondral grafts for finger joint reconstruction.

METHODS

Computer models were generated from 4 paired cadaver hands and feet and compared the radius of curvature of toe and finger articular surfaces. The angle created by the palmar divergence of adjacent condyles of the same phalanx was also compared and described as the angular difference. The distal articular surfaces of the third toe proximal and middle phalanx were compared to distal articular surfaces of all 4 finger proximal phalanges. The radius of curvature was also compared between the third toe middle phalanx base and those of all 4 fingers.

RESULTS

The toe middle phalanx medial and lateral condyles were 66% and 60% the size of the respective finger condyles. The mean angular difference between adjacent condyles of the toe middle phalanx compared to the finger was 20°. The toe proximal phalanx medial and lateral condyles were 75% and 70% the size of the respective finger condyles, with a mean angular difference between adjacent condyles of 6°. The toe middle phalanx medial base was closer in size to that of the finger (95% to 178%) compared to the toe middle phalanx lateral base (205% to 254%).

CONCLUSIONS

This study revealed that the third toe proximal phalanx distal articular surface more closely matched the geometric characteristics of the finger proximal phalanx distal articular surface than did the toe middle phalanx distal articular surface. The medial base of the toe middle phalanx more closely approximated the size of the finger middle phalanx base than did the lateral toe middle phalanx base.

CLINICAL RELEVANCE

Quantitative data have been provided to help guide third toe osteochondral donor site selection when reconstructing traumatic finger proximal interphalangeal joint defects.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Fibonacci, littler, and the hand: a brief review

In a landmark paper published in 1973, the eminent hand surgeon J. William Littler, MD, proposed two mathematical relationships between the anatomic and functional geometry of the hand. His proposal that the motion of the tips of the fingers follow an equiangular spiral has been experimentally supported. Studies have not supported his other idea that the lengths of the phalanges follow a Fibonacci series. This review, after providing the necessary mathematical background, reexamines Littler's claims, presents the associated studies, and re-evaluates their conclusions. Our analysis shows that the functional lengths of the phalanges of the little finger actually do follow a Fibonacci series and that the functional lengths of the index, long, and ring fingers follow a mathematical relative of the Fibonacci series.

Osteoarthritis of the distal interphalangeal joint

Osteoarthritis occurs with the highest prevalence in the distal interphalangeal joint of the hand and has been divided into an erosive and a nonerosive form. The pathogenesis of the early stages of osteoarthritis is poorly understood, but considerable emphasis has been placed on the role of cartilage and subchondral bone as well as soft tissue structures such as collateral ligaments and tendons. Radiographic evaluation represents the most standardized method to quantify disease progression, with different systems having been developed for defining and grading radiographic features. This current concepts article examines the recent knowledge base regarding the etiology, pathogenesis, and evaluation of osteoarthritis of the distal interphalangeal joint.

Reconstruction of the condyles of the proximal phalanx with osteochondral grafts from the ulnar base of the little finger metacarpal

PURPOSE

Traumatic defects of the condyles of the proximal phalanx (P1) are challenging injuries. Use of osteochondral grafts from the hamate had been described for defects of the base of the middle phalanx. Extending this concept, the purposes of this study were to see whether an osteochondral graft from the base of the little finger metacarpal was anatomically feasible to reconstruct a condyle of P1, and to determine whether the reconstructions performed were clinically successful.

METHODS

We measured the radius of curvature of the base of M5 and the condyles of P1 of the 4 fingers in 15 dry hand skeletons and compared them. We retrospectively reviewed 15 patients with traumatic loss of one condyle of P1. In addition, 16 osteochondral grafts from the ulnar side of the base of the M5 were harvested, tailored to reconstruct the defect, and fixed with screws. Average follow-up was 4.8 years (range, 1-7.5 y). We measured the active arc of motion of the proximal interphalangeal joint.

RESULTS

The radius of curvature of the base of M5 was 5.6 mm (range, 4.2-7.2 mm), whereas the radiuses of curvature of the condyles of P1 of the index and long fingers were 4 mm, and those of the ring and little fingers were 3.8 mm. The radius of curvature of the base of the M5 was 40% and 47% larger than that of the P1 condyles of the index-long and ring-little fingers, respectively. The active arc of motion of the proximal interphalangeal joint in the clinical cases averaged 49 degrees (range, 20 degrees to 100 degrees ). There was partial graft resorption without pain, instability, or notable loss of arc of motion. There was no severe donor-site morbidity.

CONCLUSIONS

The base of the M5 is a suitable donor site of osteochondral grafts for the condyles of P1 based on anatomical grounds. The series reported, though short and nonhomogeneous, suggests that the medium-term results of this technique are acceptable.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Two to five year follow-up of the LPM ceramic coated proximal interphalangeal joint arthroplasty

This paper presents a retrospective series of 20 LPM semi-constrained ceramic coated cobalt chrome proximal interphalangeal joint arthroplasties performed consecutively in 12 patients for arthritis of the proximal interphalangeal joint by a single surgeon between 2000 and 2004. Eleven were performed for osteoarthritis, four for post-traumatic arthritis and five for rheumatoid arthritis. Although 12 joints had an improvement in pain and an increased functional arc of movement, six joints required revision surgery for implant failure at an average of 19 months, with clinical signs of increasing pain, deteriorating motion and radiological signs of implant loosening and subsidence. This rate of revision is higher than in published series for other PIP joint implants and, therefore, close surveillance of all patients with this prosthesis currently in situ is recommended. Use of the prosthesis has ceased in this unit.

Morphology of the interphalangeal joint surface and its functional relevance

PURPOSE

To study and to clarify the curvature morphology of the articular surfaces of the proximal interphalangeal (PIP) joint and to relate joint morphology and joint kinematics.

METHODS

The radii and centers of curvature of 40 PIP joints were determined by sagittal and transverse intersections of highly precise replicas that were prepared by dental methods.

RESULTS

The PIP joint is proved to be a nonconforming joint: the articular surface of the proximal end of the middle phalanx has lesser curvatures than the condyles of the proximal phalanx. In intersections through the apex of the radial and ulnar condyles, the measured differences of the radii between the articular surfaces of the PIP joint were sagittally about 30% and transversely about 49% of the respective radii of the condyles. Incongruity of the joint results in 2 morphologically given axes for extension respective to flexion: (1) an axis given by the articular surfaces of both condyles of the proximal phalanx; and (2) a second axis given by the articular surface of the proximal end of the middle phalanx. Both articulating surfaces have 2 contact points in the transverse plane, one each, central to the apex of radial and ulnar condyles, respectively. In the middle of the joint, in the intercondylar groove, a small joint cavity was present in 37 of 40 joints.

CONCLUSIONS

The physiological incongruity of the 2 articular surfaces of the PIP joint was defined quantitatively. This allows the derivation of a theoretical model for PIP joint function that explains the kinematics and mechanical stability of the joint as well as the lubrication and nutrition of the cartilaginous structures.