Why Total Knee Replacement is necessary?

Dr L Ibobi & Dr Ph Iboyaima *

Patients with disabling knee pain, impairment of knee function and in those patients with knee pain not responding to conservative treatment generally requires Total Knee Replacement.

The knee is a large synovial joint consisting of
a) Medical compartment;
b) Lateral compartment and
c) Patello femoral compartment.

The patella is a large sesamoid bone and its function is
i) To protect the knee joint;
ii) To facilitate knee joint lubrication and
iii) To increase lever arm of the knee extensor mechanism.

There are two menisei Medial and Lateral. The menisei increase joint stability by increasing the joint concavity; act as shock absorber; contribute to joint lubrication and aid in knee rotation.

The knee is stabilized by a complex array of ligaments, tendons and soft tissues. The ligament in the medial (inner) side of the knee – Medial collateral ligament (MCL) consists of 3 layers
(a) superficial (inter)
(b) middle and
(c) deep.

The ligament on the outer side – Lateral collateral ligament consist of
(a) outer
(b) middle and
(c) deep layers.

Total Knee Replacement is indicated in those patients who experience disabling knee pain, for those patients whose radiograph (X-Ray) shows significant joint degeneration and those patients for whom non-operative treatment (e.g. oral medication, weight reduction, exercise program and assisted ambulatory devices) has failed.

Those patients who would be more appropriately treated by another surgical procedure should not be considered for total knee replacement. Absolute contraindications of Total Knee Replacement are
a) lack of a functioning extensor mechanism;
b) absence of Neurovascular control;
c) active sepsis;
d) a well functioning knee arthrodesis (fusion) and
e) a neuropathic joint (controversial).

Relative contraindications include
1) a history of knee sepsis;
2) ipsilateral osteomyelitis;
3) significant peripheral vascular disease and
4) an extended period of non-ambulatory status.

A patient with previous tubercular arthritis, who has been properly treated, can successfully undergo Total Knee Replacement.

There are many designs of Total Knee Replacement:

a) Hinged Implants: First introduced by Walldins in 1951 and made it commercially available. The unaxial hinge implant did not produce the complex motion of the knee joint. Gnepar prosthesis was designed with a posteriorly offset hinge centre of rotation.

b) Newer Hinge Prosthesis: The Kinematic Rotating Hinge (KRH) knee prosthesis by Howmedica, Rutherford, NT – a hinged device with rotating freedom.

c) Bicompartmental Prosthesis: From 1970 to 1980 – hinged implants around the anatomic approaches or the functional approaches were evolved. Gunston in 1970’s first designed polycentric knee implants which sought to produce the polycentric motion of knee joint. Robert Averill developed the dual conforming bearing mechanism with preservation of eruciates.

Coventry et al developed a two component cemented knee implant called geometric knee. The duocondylar knee having condylar shaped femoral components with metal bar in the centre. Freeman et al were the first who sacrificed both eruciates (Anterior and Posterior) ligaments and described concept of soft tissue ligament balancing.

d) Tricompartmental Prosthesis: Total condylar prosthesis was the first to replace all the condylar surfaces including patella femoral joint.

The following designs are the progressive revolutionary designs of Total Condylar Prosthesis –
i) The total condylar knee prosthesis II;
ii) The total condylar knee prosthesis III and
iii) Duopatellar Porsthesis.

Modified from Duocondylar prosthesis to include patella femoral articulation. Most of the current knee implants are either posterior cruciate retaining or substitution designs. The place of the posterior cruciate ligament in Total Knee Replacement is still controversial.

Posterior Cruciate substitution Vs Retention:

Retention:

a) Range of motion: No difference in the range of motion of the two designs in the long term;
b) Kinematics: Posterior cruciate ligament is responsible for the femoral roll back phenomenon. The P.C.L. retaining prosthesis have been shown to demonstrate paradoxical roll forward with anterior translation;
c) Gait: Many studies support the posterior cruciate ligament retaining porsthesis have a more normal gait pattern, especially during stair climbing and
d) Propioception: Simons et al – did not find any difference in the propioceptive function after posterior stabilized or cruciate retaining knees.

Meniscal bearing Prosthesis: New Jersey LCS knee – has decreasing radii of curvature of the femoral component posteriorly. Buechel and Pappas – also designed the rotating plate form design for cruciate sacrificing implants and meciseal bearing design for bicrusiate or posterior cruciate retension implants.

High Flexion TKR: This implant allows as greater than 125o of flexion. Cementless Fixation: Hungerford et al – suggested that cementless fixation would be more durable (lasting) than cemented. Ritter el al have demonstrated 96.8% survival at 20 years of cementless monoblock tibial fixation. Cementless design looks promising especially for younger patients.

Patello Femoral Design: Patellofemoral problems had been one of the greatest sources of complications in modern total knee replacement.