Literature Review

Allografting



Over the years scientists have found new techniques in fixing the on-going problem of bad knees. Most patients are people who are in sports, skiing, or having severely twisted their knee. A common problem occurs in the meniscus. The meniscus "is a c-shaped wedge of tough, rubbery cartilage in the knee about the size of a silver dollar"
(www.medfacts.com/d_trans.htm). The meniscus acts as a pillow by giving padding and reducing "the amount of friction between the thigh bone(femur) and the shin bone(tibia)" (CryoLife: Patient Information 3). Without this meniscus the femur and the tibia can come into contact creating a lot of friction by the two colliding bones. This contact causes severe pain in the knee. Some people will never get this problem fixed, but for others the pain is so excruciating that the patient must under go surgery.

Courtesy of medfacts: www.medfacts.com/d_trans.htm (x-ray)

The meniscus can be injured in many different ways. The most common way is by a sudden "[t]urning or twisting of the knee" (Schenck 28). This sudden move can cause a tear in the meniscus. The symptoms of this tear are any sudden "pain, swelling, and sometimes, a locking sensation [in the knee joint]" (CryoLife: Patient Information 3). In the past, surgeons did not think that the meniscus had any function in the knee. Once a meniscus was torn the doctor would remove the entire meniscus from the knee. However, it is now known that the meniscus serves an even greater purpose in "joint stability, lubrication and force transmission" (www.stoneclinic.com/shock.html). The meniscus helps keep the joints in tact with its full strength. The meniscus also lubricates the Tibia and the Femur, and the meniscus absorbs the bone's impact. For these reasons the meniscus is found to be very important to the life of the knee. Now there are new techniques in surgery that will allow the meniscus to be saved. The most common and simplest surgery is arthroscopic knee surgery. The process takes place where the surgeon takes tiny instruments and through two tiny incisions, one for the tool and the other for the camera, the doctor can either sew the cartilage or cut it away. The recovery for this procedure is very fast leaving patients in bed for less than five days, and doing active sports within two months. This surgery has been very effective in the Orthopedic field. If the tear takes place on the outside of the Meniscus, the lateral Meniscus, the piece has to be cut away. For instance, if the meniscus in the left knee is torn towards the left side, the lateral meniscus, that piece cannot be repaired and must be cut away. In severe cases the entire meniscus is torn; thus, the entire meniscus must be removed. For these patients they left in pain, and without a meniscus to provide padding and support.
The old strategy of removing the Meniscus entirely, without attempting to sew the Meniscus together, has proven to be very hazardous to the future of that knee. The Meniscus has a great amount of importance in the stability of the knee. Today, if the Meniscus has been removed, "it has been documented that an absence [of it] leads to severe arthritic changes in the knee joint"
(CryoLife: Patient Information 4). At this point there needs to be a procedure to somehow create a new meniscus in order to improve the chances of not receiving arthritice. Because the study is so new some doctors can only suggest getting a fake knee, where the patient will never be able to be active again. However, there has been a recent procedure that can provide a positive solution, allograft reconstruction.
Allograft reconstruction is the last and final step to meniscus surgery. In this case the meniscus is replaced with an entire new, synthetic, material that is transplanted into the knee and serves as the new meniscus. In order to take this last step the patient must have no presence of a meniscus in the knee. This is firmly established "by previous operative reports, magnetic resonance imaging [studying the tissue magnetically], or diagnostic arthroscopy [arthroscopic surgery]"
(Shelton and Dukes 324). Authroscopic surgery is a very complicated one, each step being important to the outcome of the procedure. Before the surgery there are some pre-operative planning. The knee has to have had routine radiographs, which is a type of ultra-sound to see the meniscus without having to cut into the knee. The alignment of the joint has to be measured by drawing full-length radiographs, to get an exact measurement. Arthroscopy has to have been done to determine the condition of the knee especially the anticular cartilage, this surgery must have also been taped, to give a visual of the knee and what took place during the surgery (van Arkel 591). These specific preliminary procedures are done so that the accuracy of the surgery can be precise.
Now it is time to undergo the surgery. The patient's leg is placed in a firm leg holder, "[i]t is essential that the leg holder be positioned to allow full extension and at least 120 degrees of flexion"
(Wilcox 37). This position will allow the knee joints and ligaments to be as spaced out as possible, making it easier for the doctor to get inside. After the leg is secure the patient will lay there for about forty-five minutes, under a local anesthetic. The first step in the surgery, after the incision has been made the meniscus must be prepared. The radiographs measure the size that the new meniscus must be to ensure that the new material will fit into the old place of the original meniscus. The allograft must be oversized by about 10 percent because the material will shrink after the surgery. The allografting material is preserved in a frozen tank to keep the material fresh. As soon as the allograft is thawed the ligament tissue must be removed. Then the "anterior bone anchor is cut perpendicular to the accompanying tibial plateau and sized to tightly fit a 9-mm cylindrical size". Two bone plugs are then attached to the allograft material by two no. 1 permanent braided sutures.
Figure 1:

*courtesy of Walter R. Shelton, M.D. and Andrea D. Dukes, B.S.

Once this preparation is done the prepared meniscus is placed back into the thawing material to maintain the freshness of the allograft material (Shelton and Dukes 325).
The next step is the preparation of the recipient bed, which is the old meniscal bed. The remaining old meniscus is "debrided, leaving a thin rim of vascular meniscal bed". In this process the meniscus is smoothed out to reduce any tissue problems later, like tissue build up under the allografts. Now the drilling of the tibial can take place. The tunnel is made by placing a guide pin into the old meniscal horn attachments at a forty-five degree angle. Then the hole is drilled and the tunnel is smoothed to remove any old horn meniscus tissue. The first, and outer tunnel, is complete. Then a second hole is drilled into the inner horn of the meniscus. The outer meniscal attachment has a 9-mm crater and 10-mm depth
(Shelton and Dukes 325).

Figure 2:

*courtesy of Walter R. Shelton, M.D. and Andrea D. Dukes, B.S.

Now it is time to start to transplant the allograft into the knee. One limb of the braided suture is on a flexible needle. This needle enters the knee and is fed through the drilled hole of the tibia. The suture then comes out of the bone and is left there to wait for the second suture. The second needle is then fed through the other hole and comes out of the tibia 1-cm above the other. These two sutures will help to place the allograft horns into place into the joint (Shelton and Dukes 325-326).

Figure 3:

 

Courtesy of Walter R. Shelton, M.D. and Andrea D. Dukes, B.S.

Now that the meniscus can be attached the sutures are pulled into place and the plugs are securely embedded. Once the meniscus is in the proper location the two sutures can be tied. Lastly, an additional 10-12 sutures are placed in the meniscus, in order to make sure it is secure (Shelton and Dukes 326-327).

Figure 4:






Figure 5



Courtesy of Walter R. Shelton, M.D. and Andrea D. Dukes, B.S.

Now the procedure is complete and it is time for recovery. There can be risks with this procedure, and many clinics encourage the patient to exhaust all possible options before they undergo the surgery. Because this is a new study it is better that the patient do so, but as more and more people have come out of this surgery doing well, this surgery could, in the near future, become very common. In a span of five years from 1990-1995, a total of 49 meniscal allografts were placed in 47 patients. "95-percent of patients reported a decrease in pain and an improvement in functional abilities" (Goble and Wilcox). This doctor was extremely successful with the allografting along with Dr. Carter who out of 33 patients had a 97 percent decrease in pain and 79 percent of those patients were able to increase their activity level to a more normal level, some even gain one hundred percent of their activity level (Carter 1). Therefore, the future is bright for those who are left without a meniscus, and hopefully the field will broaden.
The last concern with the use of the Allograft is how much impact the material will be able to withstand. The average meniscus (two in each knee) can "transmit 30 to 50 percent of the individual's weight"
(www.aaos.org.com). Therefore, both knees can withstand twice the weight of the person. In my experiment the allografting material will undergo many different forces, using a force sensor, to determine the maximum amount of force that the material can take. Once this is done the allograft may come closer to perfection.