Radiological positioning of a proximal interphalangeal joint resurfacing implant: Reliability and functional outcomes correlation

OBJECTIVES

The aims of this study were to define radiological measurements for quantifying the position of a surface replacing implant (CapFlex-PIP) in the proximal interphalangeal (PIP) joint, to test the reliability of these measurements, and to explore whether implant position influences patient-reported and clinical outcomes one year after surgery.

MATERIAL AND METHODS

We developed 7 radiographic measurements to quantify the position of the proximal and distal implant components. Two independent surgeons analyzed the 1-year postoperative radiographs of 63 fingers documented in our registry. Inter-rater reliability of these measurements was calculated with the intraclass correlation coefficient (ICC). Correlations between the radiographic measurements and PIP range of motion (ROM), the brief Michigan Hand Outcomes Questionnaire (MHQ), and pain were determined using Spearman's correlation coefficient. Radiographic measurements of patients with the worst and best postoperative ROM were compared using the Mann-Whitney-U test.

RESULTS

Inter-rater reliability was only good for 1 measurement (ICC = 0.89), but poor to moderate for the other measurements (ICC ranging from 0.34 to 0.69). These measurements neither correlated with ROM, brief MHQ nor pain based on correlation coefficients ranging from 0.00 to 0.31. There were no relevant differences in the radiographic measurements between patients with the worst and best ROM.

CONCLUSION

The position of the CapFlex-PIP implant could not be reliably quantified on plain radiographs. The lack of correlations between implant position and postoperative outcomes can be attributed either to the unreliable measurements or the actual lack of influence of the implant position on pain and function.

Proteoglycan 4 reduces friction more than other synovial fluid components for both cartilage-cartilage and cartilage-metal articulation

OBJECTIVE

The clinical success of focal metallic resurfacing implants depends largely on the friction between implant and opposing cartilage. Therefore, the present study determines the lubricating ability of the synovial fluid components hyaluronic acid (HA), proteoglycan 4 (PRG4) and a surface-active phospholipid (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, POPC), on the articulation between cartilage and a Cobalt Chromium Molybdenum (CoCrMo) implant surface, compared with two cartilage surfaces.

METHODS

A ring-on-disk geometry was used to perform repeated friction measurements at physiologically relevant velocities (6 and 60 mm/s) using lubricants with an increasing number of components present. Shear measurements were performed in order to evaluate the viscosity. To ensure that it is clinically relevant to explore the effect of these components, the presence of PRG4 in synovial fluid obtained from primary and revision knee and hip implant surgeries was examined.

RESULTS

PRG4 in the presence of HA was found to significantly reduce the coefficient of friction for both cartilage-cartilage and cartilage-CoCrMo interface. This is relevant, as it was also demonstrated that PRG4 is still present at the time of revision surgeries. The addition of POPC had no effect for either configurations. HA increased the viscosity of the lubricating fluid by one order of magnitude, while PRG4 and POPC had no effect.

CONCLUSION

The present study demonstrates the importance of selecting the appropriate lubrication solution to evaluate implant materials with biotribology tests. Because PRG4 is a key component for reducing friction between cartilage and an opposing surface, developing coatings which bind PRG4 is recommended for cartilage resurfacing implants.

The performance of resurfacing implants for focal cartilage defects depends on the degenerative condition of the opposing cartilage

BACKGROUND

Non-degradable resurfacing implants are being developed for treatment of focal cartilage defects. Performance of these implants has been investigated opposing intact cartilage. This study investigates whether implants would perform equally well when the opposing cartilage is fibrillated.

METHODS

Human osteochondral strips (~2x1x1 cm) with a smooth (n = 9) or fibrillated (n = 17) cartilage surface were obtained from human tibial plateaus excised during total knee arthroscopy. A custom-made pin-on-plate sliding indenter was used to apply simultaneous compression (0.75-3 MPa) and movement (4 mm/s over 6 mm). Either metal implants, polycarbonate-urethane or healthy porcine osteochondral plugs with a diameter of 6 mm were used as indenter.

FINDINGS

Cartilage roughness of the osteochondral strips was significantly higher for the fibrillated than the smooth group prior to sliding-indentation. Roughness of the indenters was not significantly altered by sliding indentation using either smooth or fibrillated cartilage. For all but one sample, sliding of smooth cartilage against any of the indenter surfaces did not cause damage. However, samples with fibrillated cartilage showed varied responses from seemingly unaffected to severe tissue wear as quantified by analysis of Indian ink staining and histology.

INTERPRETATION

This study demonstrates that the opposing cartilage quality is relevant for the clinical success of implanting an artificial implant in a focal cartilage defect. Therefore it is essential to test the efficacy of newly developed implants against arthritic joint surfaces, and care should be taken when interpreting in vivo studies in which implants are inserted in healthy joints.

Treatment of osteochondral defects: chondrointegration of metal implants improves after hydroxyapatite coating

PURPOSE

The treatment of osteochondral defects in joint cartilage remains challenging due to its limited repair capacity. This study presents a metallic osteochondral plug with hydroxyapatite (HA)-coated cap edges for improved implant-tissue contact. The hypothesis was that improved attachment prevents from synovial fluid-influx and thereby avoids osteolysis and resulting implant instability.

METHODS

In total, 24 female, adult sheep were randomized into three groups. All animals received an Episealer^®-implant in the medial condyle of the right knee. The implants were coated with two different HA versions or uncoated (control group). After 12 weeks, the implant-tissue connections were analysed radiologically and histologically.

RESULTS

In general, the groups with the coated cap edges showed a better quality of tissue connection to the implant. The occurrence of gaps between tissue and implant was more seldom, the binding of calcified and hyaline cartilage to the cap was significantly better than in the uncoated group. A histomorphometrically measured lower amount of void space in these groups compared to the group with the uncoated edges confirmed that.

CONCLUSIONS

The hypothesis of a tighter cartilage bone contact was confirmed. The HA coating of the implant's cap edges resulted in better adherence of cartilage to the implant, which was not previously reported. In conclusion, this led to a better contact between implant and cartilage as well as neighbouring bone. In clinical routine, joint fluid is aggressive, penetrates through cartilage rifts, and promotes osteolysis and loosening of implants. The observed sealing effect will act to prevent joint fluid to get access to the implant-tissue interfaces. Joint fluid is aggressive, can cause osteolysis, and can, clinically cause pain. These effects are liable to decrease with these findings and will further the longevity of these osteochondral implants.

Bone remodelling of the humerus after a resurfacing and a stemless shoulder arthroplasty

BACKGROUND

New implant designs, such as resurfacing and stemless implants, have been developed to improve the long-term outcomes of the shoulder arthroplasty. However, it is not yet fully understood if their influence on the bone load distribution can compromise the long-term stability of the implant due to bone mass changes. Using three-dimensional finite element models, the aim of the present study was to analyse the bone remodelling process of the humerus after the introduction of resurfacing and stemless implants based on the Global C.A.P. and Sidus Stem-Free designs, respectively.

METHODS

The 3D geometric model of the humerus was generated from the CT data of the Visible Human Project and the resurfacing and stemless implants were modelled in Solidworks. Considering a native humerus model, a humerus model with the resurfacing implant, and a humerus model with the stemless implant, three finite element models were developed in Abaqus. Bone remodelling simulations were performed considering healthy and poor bone quality conditions. The loading condition considered comprised 6 load cases of standard shoulder movements, including muscle and joint reaction forces estimated by a multibody model of the upper limb.

FINDINGS

The results showed similar levels of bone resorption for the resurfacing and stemless implants for common humeral regions. The regions underneath the head of the resurfacing implant, unique to this design, showed the largest bone loss. For both implants, bone resorption was more pronounced for the poor bone quality condition than for the healthy bone quality condition.

INTERPRETATION

The stemless implant lost less density at the fixation site, which might suggest that these implants may be better supported in the long-term than the resurfacing implants. However, further investigation is necessary to allow definite recommendations.