Patello-Femoral Joint Information


Patello-Femoral Joint Anatomy

 Joint is the generic name for the places in the body where two or more bones are joined together. They are also the places where the skeletal structure moves or articulates. Articular cartilage covers or encapsulates these bony surfaces. Several of the major joint systems are weight bearing. This combination of functions (movement, bone connection and weight-bearing) makes the joints some of the most susceptible areas in the body for injury and chronic pain.

Patello-Femoral Cartilage Damage

Articular cartilage is a thin, whitish, glistening layer of protective tissue that covers the joint surfaces of bones. Articular cartilage is composed of hyaline cartilage cells, which have many unique properties that allow it to function effectively as a smooth and lubricious load-bearing surface. Small defects in the articular surface can cause pain and restrict range of motion. When traumatized or injured, new hyaline cartilage cells do not replace damaged hyaline cartilage cells. Several joint diseases (e.g. rheumatoid arthritis) are complex inflammatory disease processes that slowly deteriorate the overall joint surface and often affect multiple joints at the same time. Arthrosurface's technology is not intended to treat these systemic joint diseases.

A different type of joint disease is the result of injury to a relatively small, localized area of the articular surface. These injuries create defects in the articular surface. These injuries or defects can be caused by either acute or repetitive trauma, as when one bony surface strikes against the opposing bony surface. The trauma may have occurred from athletics, a fall, car crash or other high-energy event or impact. These defects may also be caused by chronic conditions that cause the joints to load disproportionately on one side or area. These joint surfaces appear largely normal but have one or more localized lesions or defects. These defects range from a softening of the articular cartilage to complete loss of articular cartilage thus exposing the underlying bone.

Orthopedic surgeons classify the severity of the defect by assigning a grade from one to four, four being the most serious. A severe lesion (grade IV) looks like a hole or deep pockmark in an otherwise smooth, shiny articular surface. The severity (depth, size and location) of the lesion will often determine whether and what type of surgical intervention may be employed. Grade IV lesions, in particular, are defined as full-thickness defects where the underlying bone is exposed. Many physicians also believe that smaller lesions deteriorate over time and, therefore, Grade III lesions are likely to become Grade IV lesions. 

Patello-Femoral - Existing Treatments 

Marrow Stimulation Techniques 
Microfacture/Microdrilling Technique
This technique is very similar to abrasion arthroplasty except that the bleeding is initiated by impacting awls, picks or drilling directly into the bone within the lesion.

Articular defects that are larger than 15mm in diameter are generally believed to require a more aggressive intervention and are typically treated using one of the following approaches, most of which are performed as open surgery:


MosaicPlasty (OATS)
This technique was popularized in the mid-1990s. In MosaicPlasty, a series of dowel cutting instruments are used to harvest one or more cylindrical plugs or grafts of articular cartilage and bone from the surrounding healthy tissue. These tube-like grafts are then implanted into the defect site. A series of these plugs placed in close proximity to one another is used to establish a new grafted hyaline cartilage surface. A limited number of surgical institutions are performing this procedure as it is technically very challenging. Outcomes for these patients have been reported as variable based on surgeon expertise, and patient selection. In addition, pain relief has been found to be inconsistent. A lengthy post-operative regime of non-weight bearing (up to 2-6 months) and continuous passive motion has also been identified as a major contributor to the success of this procedure. 

Autologous Cell Transplantation 

ACI (Carticel®)
ACI is a therapeutic treatment whereby healthy hyaline cartilage cells are harvested from the patient, the cell counts are increased in vitro (outside the body) via some type of bioreactor expansion technique, and then those cells are injected back into the defect. This technique is still considered somewhat experimental.

Total Knee Replacement

For patients with large articular defects a procedure known as "total knee replacement" is often required. This procedure requires the removal of substantial amounts of bone followed by the implantation of a prosthetic device. Patients who undergo TKR often describe a restoration of lifestyle/activity that is profound; however, rehabilitation periods following this procedure are several months or even longer.

While the useful life of a TKR is generally claimed to be up to 20 years, clinical evidence indicates that complications can begin to arise at approximately 8 - 10 years. Each successive TKR (commonly referred to as a "revision") has been shown to have a shorter useful life than the previous implant. With each revision, the amount of remaining good quality bone stock into which the implants are anchored becomes an issue. Bone loss as a result of tissue reaction, implant loosening, implant preparation, etc., can lead to great challenges in restoring a solid anchoring site for the implant. As the revision or replacement of these devices can lead to increased morbidity (complications) and result in a very difficult rehabilitation for older patients, efforts are made to forgo the TKR procedure for as long as possible. Therefore, there is a reluctance to use TKR in patients under 60 years of age. Similar concerns and issues are prevalent in total hip replacement procedures as well. 

Resurfacing Arthroplasty

Resurfacing arthroplasty is the replacement of only the articular surface of a joint which means that only the damaged portion of the joint is resurfaced.  Therefore a smaller amount of diseased tissue is being removed when compared to a total joint.

The HemiCAP® implant is a rounded, cap-like implant made from a cobalt chrome alloy with a central post on the implanted, or bone side. Cobalt chrome is a material that has been used in total joint reconstruction devices for over two decades. This material has proven to provide a safe, effective and strong weight-bearing surface in joints. The HemiCAP® system precisely aligns the surface of the implant to the contours of the patient's articular cartilage surface, thus filling the defect and restores a smooth and continuous articulating surface.

Arthrosurface believes that the HemiCAP® implant will offer the following clinical benefits:


  • Relief from current pain and swelling

  • Return to normal activity with rapid recovery time

  • Restoration of a smooth, continuous, articulating load-bearing surface

  • A simple and reproducible outpatient/ambulatory surgical procedure

The McKeever Patellar Resurfacing Prosthesis (Howmedica®), has been used in the treatment of grade III and grade IV degenerative changes in the patellofemoral joint. This anatomically shaped polished metallic patellar device was designed to maximize the area of contact with the opposed femoral articular cartilage, and differed from other non-anatomic dome-shaped designs of that time. In a series completed from 1972 to 1985, with an average of 8.1 years follow-up, excellent results were obtained in 81% of the cases. Further, no progressive degenerative changes in the opposed femoral articular cartilage associated with the prosthetic were identified over the prolonged follow-up evaluation of up to 16 years.


Patello-Femoral - Product Overview

The Arthrosurface® HemiCAP® system is a surgical method for the treatment of localized cartilage lesions and defects in the major joints. This system is comprised of three elements; a three-dimensional mapping technology, a set of instruments to map and prepare the damaged area and a cobalt-chrome and titanium implant placed opposite to a polyethylene implant. The system precisely aligns the surface of the implant to the contours of the patient's articular cartilage surface, thus filling the defect and restoring a smooth and continuous articular surface. The HemiCAP® system has been developed so that it can be utilized via minimal access surgical techniques.

There are 2 systems that comprise the Patello-Femoral Line.  The first is the Classic Focal HemiCAP which is used for isolated and well contained lesions of the trochlea groove and the patella.  The second system is called the WAVE and is used for those patients that have more diffuse or extensive damage to their PF joint.  Both systems use the same proven intraoperative mapping technology of all HemiCAP systems.

The HemiCAP® Instrument Set enables the surgeon to accurately place the implant and precisely map the curves of the articular surface, in real-time, under direct or arthroscopic visualization, with no angle-induced errors or magnification errors that might exist with MRI, or X-ray imaging techniques.

The HemiCAP® system is intended to provide an effective interim means for managing pain and disability in the middle-aged patient until a total joint replacement treatment option becomes more necessary, and is part of a clinical treatment strategy to help avoid early-age-revision scenarios. The prosthetic may also provide a treatment option for the older patient who may not tolerate the morbidity of a total joint replacement procedure.

The HemiCAP® implants and instruments are designed to remove a minimal amount of bone stock, preserve functional structures and tissues, and allow for an uncomplicated removal in the event of revision.