Stiffened joints

Joint stiffness is common in individuals with MPS I, and the maximum range of movement of all joints may become limited. Later in the individual’s life, joint stiffness may cause pain, which may be relieved by warmth and over-the-counter painkillers. The limited movement in the shoulders and arms may make dressing difficult. Anti-inflammatory drugs can help with joint pain, but their use should be monitored closely to make sure that irritation and ulcers in the stomach do not occur. Some physicians may recommend physical therapy and range of motion exercises.

 Stiffened jointsCourtesy of E. Kakkis, MD


The shape of the hands of people with MPS I may be very noticeable and has been used as the symbol of MPS Societies. The hands are short and broad with stubby fingers. Over time, the fingers may stiffen because of GAG accumulation and inflammation. They gradually become curved, due to limited joint movement. The tips of the fingers can become permanently bent over, giving rise to the characteristic joint contractures.”

Joint Contractures Courtesy of J. E. Wraith


Like the spine, the hip joint suffers from altered bone formation. The hip is a ball-and-socket joint situated at either side of the pelvis. The “ball” is the head of the thigh bone (femur) and the “socket” is the cupped part of the pelvis (the acetabulum) that surrounds the ball. In abnormal formation of the hip (or hip dysplasia), there is a shallow acetabulum, the head of the femur is underdeveloped, and the top of the thigh bone at the neck of the femur is straightened (a condition called coxa valga). This combination of bone defects results in hip instability and sometimes dislocation.

Hip dysplasiaCourtesy Hodder/Arnold Publishers

Hip dysplasia is found to some degree in nearly all persons with the Hurler phenotype and can also be found in people on the Scheie side of the MPS I spectrum. Most children with hip dysplasia eventually require corrective hip surgery. Surgery on the hips is done more easily at a younger age, around age 5–7, for the best results. Successful surgery (i.e., surgery that is able to correct the hip dysplasia) becomes much more difficult at older ages. If the hips have already dislocated, the surgery becomes technically very difficult, and the results are much less predictable.

Without hip surgery, there is progressive pain and stiffness, and eventually dislocation of the hips, resulting in a greatly decreased ability to walk. Thus far, the results of hip surgery for people with MPS I are promising, resulting in improved motion and independent walking. Hip surgery carries a number of risks, including the risks associated with anesthesia.

An anesthetic is a medication or gas that “puts the person to sleep” before surgery. To make sure the person under anesthesia (i.e., getting an anesthetic) receives enough oxygen during the surgery, a tube is placed into the throat and connected to a machine that helps the person breathe. Individuals with MPS I are at a particularly higher risk of complications from anesthesia. Their airways are often narrow as a result of the MPS I, and the spine needs to be protected during placement of the breathing tube, making it harder to insert the breathing tube. They may also take longer to recover after anesthesia. It is important for individuals with MPS I to be assessed by their anesthesiologist (a doctor specially trained to give anesthesia) before receiving the anesthetic and to choose a hospital with experience in giving anesthesia to individuals with MPS I in order to reduce the risk of potentially serious complications.

Legs and feet

The feet of people with MPS I are broad and may be stiff with the toes curled under, rather like the hands. Many people with MPS I stand and walk with their knees and hips flexed. This, combined with a tight Achilles tendon, may cause them to walk on their toes. Some children with MPS I have knock-knees (a condition in which the knees are bent in so much they touch each other when walking) severe enough to require surgery. During this surgery, staples are placed in the bone on the inner side of the knee through a relatively small incision. These staples prevent bone growth on the inner side of the knee, allowing the outer side to catch up. As a result, the knees straighten over time, and usually, the staples are removed with a second surgery. For children too small for staples to be used, osteotomies (bone cuts) in the large bones around the knee may be required.

Physical therapy and occupational therapy

The joint stiffness and bone malformations caused by MPS I can make it hard to walk, dress, tie shoes, and do other activities. Physical therapy may help relieve symptoms and improve the person’s ability to function. Occupational therapy teaches affected individuals how to adapt to their unique daily environment.

Range-of-motion exercises (passive stretching and bending of the limbs) may offer some benefits in preserving joint function, and should be started early. Exercises that cause pain should be avoided. Once joints become significantly stiff, it may not be possible to increase the range of motion (flexibility) in the joints. However, it may still be possible to limit further losses of flexibility. It makes sense for individuals to be as active as possible to maintain joint function and improve their general health. Your or your child’s doctor or physical therapist may be able to suggest ways of achieving this through a combination of daily activities and passive range-of-motion exercises.

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