The present invention relates to diagnosis and repair of defects and damage of cartilage tissue.
Articular cartilage is a load-bearing connective tissue at the ends of long bones in synovial joints that facilitates low-friction, low-wear joint articulation. The load-bearing ability of cartilage is dependent on the presence of a large aggregating proteoglycan, aggrecan, in a matrix structure. Aggrecan is highly negatively charged due to its numerous glycosaminoglycan (GAG) side chains, and the charge density of these GAG molecules creates a swelling pressure in the interstitial fluid of cartilage that resists compression.
It is known that hydraulic permeability of osteochondral tissue, especially articular cartilage, may increase with degeneration and erosion. Progressive degeneration and erosion of articular cartilage that can occur with osteoarthritis (OA) has been correlated with increased hydraulic permeability. In addition, focal defects, which are commonly observed in the knees of symptomatic patients during arthroscopy, are discrete areas of cartilage erosion that also likely have increased hydraulic permeability. Increase in hydraulic permeability may diminish the ability of cartilage to maintain fluid pressurization, leading to larger strains on the cartilage matrix and further degeneration, as well as abnormal fluid flow and communication between the intraarticular space and the subchondral bone.
Repair strategies for cartilage defects may include arthroscopic procedures, such as microfracture; soft tissue grafts; osteochondral grafts of autogenic or allogenic source material; cell transplantation with or without a scaffold, including autologous cell implantation and mesenchymal stem cells; and synthetic and natural scaffolds. Interstitial fluid pressurization, and load-bearing capacity, may be typically restored with osteochondral graft techniques.
Determination of the possible presence and extent of cartilage defects is a critical factor in formulating a repair strategy. Clinically useful measures to diagnose the extent of cartilage degeneration and efficacy of repair strategies are limited, especially with regard to pressure maintenance within the cartilage tissue. Presently used techniques may include visual observation during arthroscopy and/or imaging modalities such as plain film x-ray attenuation, magnetic resonance imaging (MRI) and computed tomography (CT). These methods alone may produce only limited quantitative results.
While a determination of hydraulic permeability may be a valuable indicator of condition of cartilage, a direct measurement of this parameter has been performed only by experimental perfusion techniques on isolated samples of tissue in a laboratory setting. A typical ex vivo permeability measurement must be performed for a number of hours before yielding meaningful results. Indirect measurements of hydraulic permeability, extrapolated from mechanical indentation testers, have been performed, but require tissue deformation and assumptions about matrix composition that may not be applicable in damaged tissues. Direct measurement of hydraulic permeability, in situ, has heretofore not been practicable.
As can be seen, there is a need for a system that may produce quantitative information indicative of cartilage condition. In particular there is a need for a system in which a quantitative indicator of hydraulic permeability may be determined in situ.
In one aspect of the present invention, a system for assessing condition of cartilage may comprise: a contact device; a flow inducer; a fluid circuit interconnecting the contact device and the flow inducer; and a pressure sensor for determining negative pressure (−P) in the fluid circuit.
In another aspect of the present invention, a contact device for a system for assessing condition of cartilage may comprise: a flexible cap; and a flexible tube attached to the cap through which negative pressure can be applied to the cartilage when the cap is in contact with the cartilage.
In still another aspect of the present invention, a method for evaluating condition of cartilage may comprise the steps of: inducing flow of fluid from or through the cartilage; measuring negative pressure required to produce a particular flow rate of the fluid; and employing the measured negative pressure to produce a quantitative assessment of condition of the cartilage.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
Various inventive features are described below that can each be used independently of one another or in combination with other features.
The present invention generally provides a system that allows for in situ determination of hydraulic resistance to assess if a defect or damage to cartilage is present. In a particular application, the measurement system may be used in an arthroscopic setting.
Referring now to
In operation, the contact device 12 is in contact with a region of osteochondral tissue 24 such as cartilage, which may be referred to hereinafter as cartilage 24. The flow inducer 14 may be employed to produce negative pressure in the fluid circuit 22. The contact device 12 may apply this negative pressure to the cartilage 24. In response to the negative pressure, fluid 26 may flow through or out of the cartilage. The fluid 26 may comprise any one of various fluids (e.g., cartilage interstitial fluid, synovial fluid, and/or the fluid component of bone marrow) which may be present in or adjacent to the cartilage 24.
As the fluid 26 may flow out of or through the cartilage 24, it may increase overall volume of fluid in the fluid circuit 22. A rate at which this volume increases (Q) may be a function of magnitude of negative pressure (−P) in the fluid circuit 22. In other words a flow rate (i.e., Q) of the fluid 26 may be interrelated to −P. It must be noted, however, that the rate Q is not exclusively determined by the pressure level P. One factor that affects rate Q is cartilage hydraulic pressure. If the cartilage 24 has a high hydraulic resistance (i.e., low permeability), then a particular rate of flow Q may require a high magnitude of −P. Conversely, if the cartilage 24 has a low hydraulic resistance (i.e., high permeability), then the same Q may be attainable with a lower magnitude of −P. It may be seen that, by operation of the system 10, a value of hydraulic resistance (R) of a particular portion of the cartilage 24 may be quantified with a determination of two measurable parameters, −P and Q.
Referring now to
It has been found that data relating to −P may be reduced and fit to a model equation to determine R of cartilage 24 in various states of health or degeneration. Pressure values may be normalized to a baseline average pressure recorded over 5 seconds before initiation of flow. A zero time point may be set as a point at which the pressure may increase over standard deviations from the baseline average. The system 10 may be modeled in accordance with the expression:
where:
−P is averaged measured pressure over a time t;
R is hydraulic resistance of the cartilage;
C is a predetermined compliance of the system 10; and
Q is the flow rate.
In a typical measurement of cartilage condition, the time t may be selected to be consistent with a time constant of the system 10 in its operational mode. In other words, the time t may be selected to be equal to R*C. In such a case, the exponential term of Equation 1 may be exp (−1) or about 0.36. This may correspond to a time t at which −P may be at about 64% of its final value. When the time t is selected to be equal to the time constant, the system 10 may be operated in a manner that may clinically optimized. In other words, values of −P may be readily discernible for comparative purposes but time lapse for performing a measurement may remain desirably low. For example, it has been found that an optimum time for performing a particular measurement sequence with an exemplary embodiment of the system 10 may be about 20 seconds.
Referring now to
In operation, the contact device 12 may be applied to cartilage in any one of numerous clinical settings, such as open-joint surgery or arthroscopic surgery. The system 10 may be employed during a procedure to determine, in “real time” whether a patient's cartilage is healthy or defective. The contact device may be applied to a particular portion of the patient's cartilage and, within about 20 seconds, a clinician may be able to see a quantitative display of R on the display unit 20. In this context, the system 10 may be employed as an adjunct to a cartilage repair procedure. Because cartilage condition may be determined in “real-time”, repair strategy decisions may be made based on quantitative assessment of cartilage conditions.
Referring now to
Referring now to
In a step 604, the contact device may be placed in contact with a portion of cartilage of a patient (e.g., the contact device 12 may be inserted through an arthroscopic cannula and into contact with the cartilage 24 during an arthroscopic diagnostic and repair procedure). In a step 606, flow may be induced in the fluid circuit (e.g., the flow inducer 14 may be operated to induce a volume change of the system 10 at a rate Q; the rate Q may be predetermined and constant. Alternatively, the rate Q may be variable in which case the variable rate Q may be continuously transmitted to the processor 18). In a step 608, negative pressure in the system may be measured for a time t (e.g., the pressure sensor 16 may sense −P over a time period that corresponds to a time constant of the system 10). In a step 610, −P data may be processed to produce an R value (e.g., average −P collected over the time t may be processed in accordance with the Equation 1 in the processor 18 to yield an R value for a particular portion of the cartilage 24). In step 612, the R value may be displayed (e.g., the processor 18 may produce a signal to the display unit 20 so that the display unit 20 may display the R value to a clinician).
It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
This application claims the priority date of U.S. Provisional Application No. 61/249,339 filed Oct. 7, 2009.
This invention was made with Government support under AR044058 awarded by NIH. The Government has certain rights in the invention.
Number | Date | Country | |
---|---|---|---|
61249339 | Oct 2009 | US |