Joint Compression Therapy in the Prevention of Osteopenia of Prematurity:Current Research and Future Considerations
Year: 2011

Osteopenia of prematurity is a metabolic bone disease affecting neonates born during the second trimester of pregnancy and classified as very low birth weight, or less than 1500 grams at birth. Improvements in neonatal nutrition have reduced osteopenia of prematurity by increasing available calcium, phosphorus, magnesium and vitamin D for bone mineralization. Ossification also requires the presence of adequate bone matrix for mineralization to be completed. Passive mechanical stimulation such as joint compression replicates the resistance and weight bearing movements of the fetus in utero. Fetal osteoprogenitor cells are signaled to develop into osteoblasts, thus creating bone matrix which can then be mineralized. Research into the effects of passive physical exercise with joint compression on the prevention of osteopenia of prematurity are compared and discussed to ascertain recommendations for future implementation and considerations.  grams, qualifying them as very low birth weight (VLBW) infants. In the vast majority of cases, VLBW designation also corresponds to a gestational birth age of less than 32 weeks (Hamilton, Martin, Ventura, 2010) Among the many potential consequences is osteopenia of prematurity (OOP) which affects approximately 30% of premature, VLBW neonates (Cross Vasquez, 2009) OOP is described as a loss of bone density resulting from suboptimal bone mineralization (Lam, So, Ng, 2007) OOP should not be considered expected sequelae of VLBW birth, nor is it without its own consequences. OOP can produce soft, unstable bones unsuitable for maintaining normal physical structure. In particular, a neonate with severe chronic lung disease may not have the structural strength of the ribs to keep the chest wall from pressing down onto the lungs, making it even more difficult to wean off a ventilator (Williford, Pare, Carlson, 2008) An osteopenic neonate is susceptible to fractures with normal handling during routine care. The neonate can sustain loss of function and pain from the fractures (Williford, Pare, Carlson, 2008) OOP negatively impacts neonatal growth rate (Mitchell, Rogers, Hicks, Hawthorne, Parker, Abrams, 2009) Severe OOP with alkaline phosphotase levels 1200 IU/ml have been associated with reduced linear growth at 18 months of age (Demarini, 2005) Normal Physiology Related to Term Gestation Fetal ossification of strong, stable bones is strongly influenced by movement (Lam, So, Ng, 2007) Bone structure follows function, and a variety of stressors from joint impact (weight bearing) to mechanical pull increases both length and cortical thickness (So Ng, 2005) By the end of the second trimester (approximately 28 weeks gestation) the fetus can move up to thirty times per hour (Nihira, 2009) The muscular walls of the uterus acts as resistance to provide JOINT COMPRESSION THERAPY/PREVENTION OF OOP 4 weight bearing experiences for the fetus as the arms and legs extend, then recoil back to flexed positions. In addition, the mother moves and changes positions throughout the day. This activity changes the plane of movement for the fetus, creating differing mechanical strains on muscles (Land Schoenau, 2008) Physical activity and weight bearing/resistance movement signals bone forming cells called osteoblasts to secrete bone matrix according to areas being stressed by function. Once surrounded by matrix, osteoblasts are considered mature bone cells, or osteocytes. The final step of stable bone formation is mineralization via deposition of calcium, phosphorus and magnesium (Rauch Schoenau, 2002) Mineralization depends on proper nutritional intake, gastrointestinal absorption into the bloodstream, and presence of vitamin D to assist the regulation of these processes (Demarini, 2005) The fetus is dependent upon the mother for all nutrients throughout the pregnancy. Beginning in the second trimester, an increasing amount of calcium crosses the placenta and enters fetal circulation (Rauch Schoenau, 2002) However, the vast majority of mineral exchange occurs in the third trimester, peaking at 36 38 weeks gestation (Williford, Pare, Carlson, 2008) At this point, large amounts of calcium are flowing into the fetus creating fetal serum calcium levels approximately five times higher than maternal serum calcium levels. Fetal serum phosphorus levels also increase in the third trimester (Cross Vasquez, 2009) During this time, the fetus is actively mineralizing strong, stable bones as well as storing extra calcium and phosphorus in the bones. This is necessary biologically as the maternal to fetal hypercalcemic circulation is abruptly halted at delivery when the umbilical cord is cut (Land Schoenau, 2008) JOINT COMPRESSION THERAPY/PREVENTION OF OOP 5 After birth the term newborn ingests very little at breast for the first two or three days. Thereafter, maternal breastmilk contains much less calcium than the rich blood supply in utero. It is during this time the extra mineral stores are slowly released from the bones to maintain adequate serum levels (Williford, Pare, Carlson, 2008) Specifically, low serum calcium levels trigger the release of parathyroid hormone (PTH) PTH signals another type of bone cell, the osteoclast, to release calcium into the bloodstream by breaking down or "remodeling" areas of bone (Land Schoenau, 2008) Pathophysiology Related to Preterm, VLBW Neonates The greatest risk of OOP for the VLBW neonate results from the lack of mineral store deposition during the third trimester (Eliakim Nemet, 2005) Lacking exposure to the calciumrich maternal/placental circulation, the premature infant begins life at a distinct disadvantage: Though typical for gestational age, the VLBW neonate has relatively unstable bones. In addition, the neonate has little in the way of extra calcium and phosphorus stores from which to draw in order to meet the needs of bone mineralization (So Ng, 2005) A preterm, VLBW neonate faces a host of other contributing factors which can increase the risk and severity of OOP. The VLBW neonate is not likely to tolerate full enteral feedings within the first week of life. Intravenous nutrition in the form of total parenteral nutrition (TPN) is minimally capable of supplying optimal daily intake of calcium and phosphorus (So Ng, 2005) Even centrally infusing TPN cannot deliver the daily recommended amounts of minerals for VLBW neonates. Reasons vary and include limits on calcium:phosphorus solubility (Lam, So, Ng, 2007) JOINT COMPRESSION THERAPY/PREVENTION OF OOP 6 Almost all VLBW neonates are treated with fluid restrictions which further limit the mineral inclusion in the TPN recipe (So Ng, 2005) This factor becomes more pronounced if IV access is peripheral only. Many NICUs do not infuse calcium peripherally. An NICU which opts to infuse calcium peripherally should do so in small amounts to minimize risk of infiltration associated tissue sloughing (Abrams, 2008) A provider would still be unable to administer enough to meet the neonate's daily needs. A VLBW neonate is at higher risk to remain on TPN for a prolonged period of time. Reasons include feeding intolerance of unknown etiology, intestinal dysmotility, septicemia requiring a hold on enteral feeds, and/or necrotizing enterocolitis (So Ng, 2005) The optimal solution is a transition to enteral feedings as soon as possible (Cross Vasquez, 2009) Appropriate enteral feedings consist of breastmilk fortified with a powder additive delivering additional calcium, phosphorus and calories equally 24 calories per ounce. A formula alternative would be a specialized premature infant formula containing higher levels of calcium and phosphorus, also providing 24 calories per ounce (Eliakim Nemet, 2005) Unfortunately, some VLBW neonates do not initially tolerate fortified, higher calorie feedings. Unfortified breastmilk and premature formula do not provide the requisite amount of mineral intake (So Ng, 2008) Routinely prescribed medications can negatively affect the neonate's ability to properly mineralize bone matrix. Furosemide is known to cause hypercalcuria and nephrocalcinosis. Furosemide signals the kidneys to filter calcium out of the bloodstream and excrete it (Cross Vasquez, 2009) As the serum calcium level drops, PTH rises and osteoclasts begin to remodel bone to maintain serum calcium levels. Methylxanthines and glucocorticoids are also implicated as risk factors for the development of OOP (So Ng, 2005) JOINT COMPRESSION THERAPY/PREVENTION OF OOP 7 One of the most overlooked contributing factors of OOP is physical movement. As part of neonatal developmental care, a significant effort has been made to promote flexion predominant positioning, boundaries, and a "hands off" approach towards neonatal care (Eliakim Nemet, 2005) In reality, neonates in utero are exposed to muffled noises, shades of light, exterior movement from the mother, and self movement within a tactile environment. After birth, the VLBW neonate is no longer able to move freely within a buoyant environment, experiencing positional changes as the mother goes about daily life. The VLBW neonate is subjected to the forces of gravity in the NICU (Demarini, 2005) Instead of free floating, weight bearing extension/flexion, the neonate experiences restricted movement via gravitational pull (Rauch Schoenau, 2002) Indeed, this difference between in utero and ex utero movement diminishes the VLBW neonate's ability to engage the body's system of function/structure ossification (Land Schoenau, 2008) A decrease in function decreases osteoblast activity, thus creating less osteiod structure to mineralize even if optimal calcium, phosphorus, magnesium and vitamin D intake are provided (Rauch Schoenau, 2002) Physical exercise programs including joint compression ar